diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6b776c7..f6690dc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 ### 0.5.2
 
 - Fix rename field on the field add. (#134)
+- Fix postgres field type change error. (#135)
 
 ### 0.5.1
 
diff --git a/README.md b/README.md
index acb68bc..9cf823a 100644
--- a/README.md
+++ b/README.md
@@ -8,11 +8,7 @@
 ## Introduction
 
 Aerich is a database migrations tool for Tortoise-ORM, which is like alembic for SQLAlchemy, or like Django ORM with
-it\'s own migrations solution.
-
-~~**Important: You can only use absolutely import in your `models.py` to make `aerich` work.**~~
-
-From version `v0.5.0`, there is no such limitation now.
+it\'s own migration solution.
 
 ## Install
 
@@ -97,8 +93,8 @@ Success create app migrate location ./migrations/models
 Success generate schema for app "models"
 ```
 
-If your Tortoise-ORM app is not the default `models`, you must specify the correct app via `--app`, e.g. `aerich
---app other_models init-db`.
+If your Tortoise-ORM app is not the default `models`, you must specify the correct app via `--app`,
+e.g. `aerich --app other_models init-db`.
 
 ### Update models and make migrate
 
@@ -193,8 +189,7 @@ Inspect a specified table in the default app and redirect to `models.py`:
 aerich inspectdb -t user > models.py
 ```
 
-Note that this command is limited and cannot infer some fields, such as `IntEnumField`, `ForeignKeyField`, and
-others.
+Note that this command is limited and cannot infer some fields, such as `IntEnumField`, `ForeignKeyField`, and others.
 
 ### Multiple databases
 
@@ -213,12 +208,6 @@ tortoise_orm = {
 
 You only need to specify `aerich.models` in one app, and must specify `--app` when running `aerich migrate` and so on.
 
-## Support this project
-
-| AliPay                                                                                 | WeChatPay                                                                                 | PayPal                                                           |
-| -------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------- | ---------------------------------------------------------------- |
-| <img width="200" src="https://github.com/long2ice/aerich/raw/dev/images/alipay.jpeg"/> | <img width="200" src="https://github.com/long2ice/aerich/raw/dev/images/wechatpay.jpeg"/> | [PayPal](https://www.paypal.me/long2ice) to my account long2ice. |
-
 ## License
 
 This project is licensed under the
diff --git a/aerich/ddl/postgres/__init__.py b/aerich/ddl/postgres/__init__.py
index 415489d..d5282cd 100644
--- a/aerich/ddl/postgres/__init__.py
+++ b/aerich/ddl/postgres/__init__.py
@@ -12,7 +12,9 @@ class PostgresDDL(BaseDDL):
     _ADD_INDEX_TEMPLATE = 'CREATE {unique}INDEX "{index_name}" ON "{table_name}" ({column_names})'
     _DROP_INDEX_TEMPLATE = 'DROP INDEX "{index_name}"'
     _ALTER_NULL_TEMPLATE = 'ALTER TABLE "{table_name}" ALTER COLUMN "{column}" {set_drop} NOT NULL'
-    _MODIFY_COLUMN_TEMPLATE = 'ALTER TABLE "{table_name}" ALTER COLUMN "{column}" TYPE {datatype}'
+    _MODIFY_COLUMN_TEMPLATE = (
+        'ALTER TABLE "{table_name}" ALTER COLUMN "{column}" TYPE {datatype}{using}'
+    )
     _SET_COMMENT_TEMPLATE = 'COMMENT ON COLUMN "{table_name}"."{column}" IS {comment}'
     _DROP_FK_TEMPLATE = 'ALTER TABLE "{table_name}" DROP CONSTRAINT "{fk_name}"'
 
@@ -27,10 +29,13 @@ class PostgresDDL(BaseDDL):
     def modify_column(self, model: "Type[Model]", field_describe: dict, is_pk: bool = False):
         db_table = model._meta.db_table
         db_field_types = field_describe.get("db_field_types")
+        db_column = field_describe.get("db_column")
+        datatype = db_field_types.get(self.DIALECT) or db_field_types.get("")
         return self._MODIFY_COLUMN_TEMPLATE.format(
             table_name=db_table,
-            column=field_describe.get("db_column"),
-            datatype=db_field_types.get(self.DIALECT) or db_field_types.get(""),
+            column=db_column,
+            datatype=datatype,
+            using=f' USING "{db_column}"::{datatype}',
         )
 
     def set_comment(self, model: "Type[Model]", field_describe: dict):
diff --git a/aerich/migrate.py b/aerich/migrate.py
index 95700cd..8f842fe 100644
--- a/aerich/migrate.py
+++ b/aerich/migrate.py
@@ -392,6 +392,9 @@ class Migrate:
                         elif option == "default":
                             # change column default
                             cls._add_operator(cls._alter_default(model, new_data_field), upgrade)
+                        elif option == "unique":
+                            # because indexed include it
+                            pass
                         else:
                             # modify column
                             cls._add_operator(
diff --git a/images/alipay.jpeg b/images/alipay.jpeg
deleted file mode 100644
index c2b63b4..0000000
Binary files a/images/alipay.jpeg and /dev/null differ
diff --git a/images/wechatpay.jpeg b/images/wechatpay.jpeg
deleted file mode 100644
index c2618e4..0000000
Binary files a/images/wechatpay.jpeg and /dev/null differ
diff --git a/tests/test_ddl.py b/tests/test_ddl.py
index ea5d0ec..c5f1c6e 100644
--- a/tests/test_ddl.py
+++ b/tests/test_ddl.py
@@ -76,7 +76,10 @@ def test_modify_column():
     if isinstance(Migrate.ddl, MysqlDDL):
         assert ret0 == "ALTER TABLE `category` MODIFY COLUMN `name` VARCHAR(200)"
     elif isinstance(Migrate.ddl, PostgresDDL):
-        assert ret0 == 'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200)'
+        assert (
+            ret0
+            == 'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200) USING "name"::VARCHAR(200)'
+        )
 
     if isinstance(Migrate.ddl, MysqlDDL):
         assert (
@@ -84,7 +87,9 @@ def test_modify_column():
             == "ALTER TABLE `user` MODIFY COLUMN `is_active` BOOL NOT NULL  COMMENT 'Is Active' DEFAULT 1"
         )
     elif isinstance(Migrate.ddl, PostgresDDL):
-        assert ret1 == 'ALTER TABLE "user" ALTER COLUMN "is_active" TYPE BOOL'
+        assert (
+            ret1 == 'ALTER TABLE "user" ALTER COLUMN "is_active" TYPE BOOL USING "is_active"::BOOL'
+        )
 
 
 def test_alter_column_default():
diff --git a/tests/test_migrate.py b/tests/test_migrate.py
index ad90a85..54d806d 100644
--- a/tests/test_migrate.py
+++ b/tests/test_migrate.py
@@ -768,7 +768,7 @@ def test_migrate(mocker: MockerFixture):
     - alter default: Config.status
     - rename column: Product.image -> Product.pic
     """
-    mocker.patch("click.prompt", side_effect=(False, True))
+    mocker.patch("click.prompt", side_effect=(True,))
 
     models_describe = get_models_describe("models")
     Migrate.app = "models"
@@ -798,7 +798,6 @@ def test_migrate(mocker: MockerFixture):
                 "ALTER TABLE `product` ALTER COLUMN `view_num` SET DEFAULT 0",
                 "ALTER TABLE `user` DROP COLUMN `avatar`",
                 "ALTER TABLE `user` MODIFY COLUMN `password` VARCHAR(100) NOT NULL",
-                "ALTER TABLE `user` MODIFY COLUMN `username` VARCHAR(20) NOT NULL",
                 "CREATE TABLE IF NOT EXISTS `newmodel` (\n    `id` INT NOT NULL PRIMARY KEY AUTO_INCREMENT,\n    `name` VARCHAR(50) NOT NULL\n) CHARACTER SET utf8mb4;",
                 "ALTER TABLE `user` ADD UNIQUE INDEX `uid_user_usernam_9987ab` (`username`)",
                 "CREATE TABLE `email_user` (`email_id` INT NOT NULL REFERENCES `email` (`email_id`) ON DELETE CASCADE,`user_id` INT NOT NULL REFERENCES `user` (`id`) ON DELETE CASCADE) CHARACTER SET utf8mb4",
@@ -823,7 +822,6 @@ def test_migrate(mocker: MockerFixture):
                 "ALTER TABLE `user` ADD `avatar` VARCHAR(200) NOT NULL  DEFAULT ''",
                 "ALTER TABLE `user` DROP INDEX `idx_user_usernam_9987ab`",
                 "ALTER TABLE `user` MODIFY COLUMN `password` VARCHAR(200) NOT NULL",
-                "ALTER TABLE `user` MODIFY COLUMN `username` VARCHAR(20) NOT NULL",
                 "DROP TABLE IF EXISTS `email_user`",
                 "DROP TABLE IF EXISTS `newmodel`",
             ]
@@ -832,8 +830,8 @@ def test_migrate(mocker: MockerFixture):
     elif isinstance(Migrate.ddl, PostgresDDL):
         assert sorted(Migrate.upgrade_operators) == sorted(
             [
-                'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200)',
-                'ALTER TABLE "category" ALTER COLUMN "slug" TYPE VARCHAR(100)',
+                'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200) USING "name"::VARCHAR(200)',
+                'ALTER TABLE "category" ALTER COLUMN "slug" TYPE VARCHAR(100) USING "slug"::VARCHAR(100)',
                 'ALTER TABLE "config" ADD "user_id" INT NOT NULL',
                 'ALTER TABLE "config" ADD CONSTRAINT "fk_config_user_17daa970" FOREIGN KEY ("user_id") REFERENCES "user" ("id") ON DELETE CASCADE',
                 'ALTER TABLE "config" ALTER COLUMN "status" DROP DEFAULT',
@@ -843,11 +841,10 @@ def test_migrate(mocker: MockerFixture):
                 'ALTER TABLE "email" RENAME COLUMN "id" TO "email_id"',
                 'ALTER TABLE "email" DROP CONSTRAINT "fk_email_user_5b58673d"',
                 'CREATE INDEX "idx_email_email_4a1a33" ON "email" ("email")',
-                'ALTER TABLE "user" ALTER COLUMN "username" TYPE VARCHAR(20)',
                 'CREATE UNIQUE INDEX "uid_product_name_f14935" ON "product" ("name", "type")',
                 'ALTER TABLE "product" ALTER COLUMN "view_num" SET DEFAULT 0',
                 'ALTER TABLE "user" DROP COLUMN "avatar"',
-                'ALTER TABLE "user" ALTER COLUMN "password" TYPE VARCHAR(100)',
+                'ALTER TABLE "user" ALTER COLUMN "password" TYPE VARCHAR(100) USING "password"::VARCHAR(100)',
                 'CREATE TABLE IF NOT EXISTS "newmodel" (\n    "id" SERIAL NOT NULL PRIMARY KEY,\n    "name" VARCHAR(50) NOT NULL\n);\nCOMMENT ON COLUMN "config"."user_id" IS \'User\';',
                 'CREATE UNIQUE INDEX "uid_user_usernam_9987ab" ON "user" ("username")',
                 'CREATE TABLE "email_user" ("email_id" INT NOT NULL REFERENCES "email" ("email_id") ON DELETE CASCADE,"user_id" INT NOT NULL REFERENCES "user" ("id") ON DELETE CASCADE)',
@@ -855,10 +852,9 @@ def test_migrate(mocker: MockerFixture):
         )
         assert sorted(Migrate.downgrade_operators) == sorted(
             [
-                'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200)',
-                'ALTER TABLE "category" ALTER COLUMN "slug" TYPE VARCHAR(200)',
-                'ALTER TABLE "user" ALTER COLUMN "password" TYPE VARCHAR(200)',
-                'ALTER TABLE "user" ALTER COLUMN "username" TYPE VARCHAR(20)',
+                'ALTER TABLE "category" ALTER COLUMN "name" TYPE VARCHAR(200) USING "name"::VARCHAR(200)',
+                'ALTER TABLE "category" ALTER COLUMN "slug" TYPE VARCHAR(200) USING "slug"::VARCHAR(200)',
+                'ALTER TABLE "user" ALTER COLUMN "password" TYPE VARCHAR(200) USING "password"::VARCHAR(200)',
                 'ALTER TABLE "config" DROP COLUMN "user_id"',
                 'ALTER TABLE "config" DROP CONSTRAINT "fk_config_user_17daa970"',
                 'ALTER TABLE "config" ALTER COLUMN "status" SET DEFAULT 1',