diff --git a/api/alembic/versions/3c3d09cd858f_make_storage_backends_workspace_id_nullable.py b/api/alembic/versions/3c3d09cd858f_make_storage_backends_workspace_id_nullable.py
new file mode 100644
index 0000000..3e8b3f6
--- /dev/null
+++ b/api/alembic/versions/3c3d09cd858f_make_storage_backends_workspace_id_nullable.py
@@ -0,0 +1,56 @@
+"""Make storage_backends workspace_id nullable
+
+将 storage_backends 表的 workspace_id 字段设置为可选
+
+Revision ID: 3c3d09cd858f
+Revises: b14d95497d4f
+Create Date: 2026-01-31 17:16:54.726838
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+# 修订标识符，由 Alembic 使用
+revision: str = "3c3d09cd858f"
+down_revision: Union[str, Sequence[str], None] = "b14d95497d4f"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema.
+
+    升级数据库架构：将 storage_backends 表的 workspace_id 字段改为可空
+    允许存储后端不绑定到特定工作空间
+    """
+    # ### commands auto generated by Alembic - please adjust! ###
+    # 修改 storage_backends 表的 workspace_id 列，允许为空
+    op.alter_column(
+        "storage_backends",
+        "workspace_id",
+        existing_type=sa.VARCHAR(length=36),
+        nullable=True,
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema.
+
+    降级数据库架构：将 storage_backends 表的 workspace_id 字段改为不可空
+    回退到要求存储后端必须绑定到工作空间的状态
+    """
+    # ### commands auto generated by Alembic - please adjust! ###
+    # 修改 storage_backends 表的 workspace_id 列，设置为不可空
+    op.alter_column(
+        "storage_backends",
+        "workspace_id",
+        existing_type=sa.VARCHAR(length=36),
+        nullable=False,
+    )
+    # ### end Alembic commands ###
diff --git a/api/app/models.py b/api/app/models.py
index 74f7f29..b212561 100644
--- a/api/app/models.py
+++ b/api/app/models.py
@@ -246,7 +246,7 @@ class StorageBackendConfig(Base):
     id = Column(
         String(36), primary_key=True, index=True, default=lambda: str(uuid.uuid4())
     )
-    workspace_id = Column(String(36), ForeignKey("workspaces.id"), nullable=False)
+    workspace_id = Column(String(36), ForeignKey("workspaces.id"), nullable=True)
     name: Mapped[str] = mapped_column(String, unique=True, nullable=False, index=True)
     backend_type: Mapped[str] = mapped_column(String, nullable=False)  # local or s3
     is_active: Mapped[bool] = mapped_column(Integer, default=0)  # 0: False, 1: True