diff --git a/src/core/db.py b/src/core/db.py
new file mode 100644
index 0000000..728f35d
--- /dev/null
+++ b/src/core/db.py
@@ -0,0 +1,25 @@
+"""ChromaDB 数据库层."""
+import chromadb
+from chromadb.api.models.Collection import Collection
+
+
+class VectorDB:
+    """向量数据库封装."""
+
+    def __init__(self, persist_dir: str = "./data"):
+        self.client = chromadb.PersistentClient(path=persist_dir)
+
+    def get_or_create_collection(self, name: str) -> Collection:
+        """获取或创建 collection."""
+        return self.client.get_or_create_collection(name=name)
+
+    def delete_collection(self, name: str) -> None:
+        """删除 collection."""
+        try:
+            self.client.delete_collection(name=name)
+        except ValueError:
+            pass  # collection 不存在则忽略
+
+    def close(self) -> None:
+        """释放数据库连接."""
+        self.client.close()
diff --git a/tests/test_db.py b/tests/test_db.py
new file mode 100644
index 0000000..f217e95
--- /dev/null
+++ b/tests/test_db.py
@@ -0,0 +1,48 @@
+"""数据库层测试."""
+import gc
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from src.core.db import VectorDB
+
+
+class TestVectorDB:
+    """VectorDB 测试."""
+
+    @pytest.fixture
+    def temp_dir(self):
+        with tempfile.TemporaryDirectory(ignore_cleanup_errors=True) as d:
+            yield d
+
+    def test_init_creates_persist_directory(self, temp_dir):
+        """初始化时自动创建持久化目录."""
+        db = VectorDB(persist_dir=temp_dir + "/subdir")
+        assert Path(temp_dir + "/subdir").exists()
+        assert db.client is not None
+
+    def test_get_or_create_collection(self, temp_dir):
+        """创建或获取 collection."""
+        db = VectorDB(persist_dir=temp_dir)
+        col = db.get_or_create_collection("test_col")
+        assert col.name == "test_col"
+
+        # 再次获取应返回同一个
+        col2 = db.get_or_create_collection("test_col")
+        assert col2.name == "test_col"
+
+    def test_count_returns_zero_for_empty_collection(self, temp_dir):
+        """空 collection 文档数为 0."""
+        db = VectorDB(persist_dir=temp_dir)
+        col = db.get_or_create_collection("test_col")
+        assert col.count() == 0
+
+    def test_delete_collection(self, temp_dir):
+        """删除 collection."""
+        db = VectorDB(persist_dir=temp_dir)
+        db.get_or_create_collection("tmp_col")
+        db.delete_collection("tmp_col")
+        # 再次获取会创建新的
+        col = db.get_or_create_collection("tmp_col")
+        assert col.count() == 0