diff --git a/backend/app/search_client.py b/backend/app/search_client.py
new file mode 100644
index 0000000..bfa9650
--- /dev/null
+++ b/backend/app/search_client.py
@@ -0,0 +1,43 @@
+import base64
+
+
+def _encode_key(key: str) -> str:
+    return base64.urlsafe_b64encode(key.encode("utf-8")).decode("ascii").rstrip("=")
+
+
+class SearchClient:
+    def __init__(self, client, index_name: str):
+        self._client = client
+        self._index_name = index_name
+
+    def index_document(self, key: str, path: str, title: str, content: str) -> None:
+        index = self._client.index(self._index_name)
+        index.add_documents([{
+            "id": _encode_key(key),
+            "key": key,
+            "path": path,
+            "title": title,
+            "content": content,
+        }])
+
+    def delete_document(self, key: str) -> None:
+        index = self._client.index(self._index_name)
+        index.delete_document(_encode_key(key))
+
+    def search(self, query: str) -> list[dict]:
+        index = self._client.index(self._index_name)
+        response = index.search(query, {
+            "attributesToHighlight": ["content"],
+            "highlightPreTag": "<em>",
+            "highlightPostTag": "</em>",
+        })
+        results = []
+        for hit in response.get("hits", []):
+            formatted = hit.get("_formatted", {})
+            results.append({
+                "key": hit["key"],
+                "title": hit["title"],
+                "path": hit["path"],
+                "snippet": formatted.get("content", hit.get("content", "")),
+            })
+        return results
diff --git a/backend/tests/test_search_client.py b/backend/tests/test_search_client.py
new file mode 100644
index 0000000..6d75f63
--- /dev/null
+++ b/backend/tests/test_search_client.py
@@ -0,0 +1,80 @@
+from app.search_client import SearchClient
+
+
+class FakeIndex:
+    def __init__(self):
+        self.documents = {}
+        self.deleted_ids = []
+
+    def add_documents(self, docs):
+        for doc in docs:
+            self.documents[doc["id"]] = doc
+
+    def delete_document(self, doc_id):
+        self.documents.pop(doc_id, None)
+        self.deleted_ids.append(doc_id)
+
+    def search(self, query, params=None):
+        hits = []
+        for doc in self.documents.values():
+            if query in doc["content"] or query in doc["title"]:
+                formatted = dict(doc)
+                if query in doc["content"]:
+                    formatted["content"] = doc["content"].replace(query, f"<em>{query}</em>")
+                hits.append({**doc, "_formatted": formatted})
+        return {"hits": hits}
+
+
+class FakeMeilisearchSDK:
+    def __init__(self):
+        self.indexes = {}
+
+    def index(self, name):
+        if name not in self.indexes:
+            self.indexes[name] = FakeIndex()
+        return self.indexes[name]
+
+
+def test_index_document_adds_document_with_encoded_id():
+    sdk = FakeMeilisearchSDK()
+    client = SearchClient(sdk, index_name="documents")
+
+    client.index_document(
+        "产品文档/架构设计.md", "产品文档", "架构设计.md", "DocHub 使用 MinIO 存储文档"
+    )
+
+    index = sdk.indexes["documents"]
+    assert len(index.documents) == 1
+    stored = list(index.documents.values())[0]
+    assert stored["key"] == "产品文档/架构设计.md"
+    assert stored["path"] == "产品文档"
+    assert stored["title"] == "架构设计.md"
+    assert stored["content"] == "DocHub 使用 MinIO 存储文档"
+
+
+def test_delete_document_removes_document():
+    sdk = FakeMeilisearchSDK()
+    client = SearchClient(sdk, index_name="documents")
+    client.index_document("产品文档/旧文档.md", "产品文档", "旧文档.md", "旧内容")
+
+    client.delete_document("产品文档/旧文档.md")
+
+    index = sdk.indexes["documents"]
+    assert index.documents == {}
+    assert len(index.deleted_ids) == 1
+
+
+def test_search_returns_matching_documents_with_highlighted_snippet():
+    sdk = FakeMeilisearchSDK()
+    client = SearchClient(sdk, index_name="documents")
+    client.index_document(
+        "产品文档/架构设计.md", "产品文档", "架构设计.md", "DocHub 支持全文检索功能"
+    )
+
+    results = client.search("检索")
+
+    assert len(results) == 1
+    assert results[0]["key"] == "产品文档/架构设计.md"
+    assert results[0]["title"] == "架构设计.md"
+    assert results[0]["path"] == "产品文档"
+    assert "<em>检索</em>" in results[0]["snippet"]