diff --git a/AnnService/inc/IndexBuilder/Options.h b/AnnService/inc/IndexBuilder/Options.h
index 7c939efae..f35d6099e 100644
--- a/AnnService/inc/IndexBuilder/Options.h
+++ b/AnnService/inc/IndexBuilder/Options.h
@@ -29,6 +29,8 @@ class BuilderOptions : public Helper::ArgumentsParser
 
     std::string m_vectorDelimiter;
 
+    bool m_append;
+
     SPTAG::VectorValueType m_inputValueType;
 
     std::string m_inputFiles;
diff --git a/AnnService/src/IndexBuilder/Options.cpp b/AnnService/src/IndexBuilder/Options.cpp
index d0fcd0fd8..45c1a5f52 100644
--- a/AnnService/src/IndexBuilder/Options.cpp
+++ b/AnnService/src/IndexBuilder/Options.cpp
@@ -23,6 +23,7 @@ BuilderOptions::BuilderOptions()
     AddRequiredOption(m_outputFolder, "-o", "--outputfolder", "Output folder.");
     AddRequiredOption(m_indexAlgoType, "-a", "--algo", "Index Algorithm type.");
     AddOptionalOption(m_builderConfigFile, "-c", "--config", "Config file for builder.");
+    AddOptionalOption(m_append, "-p", "--append", "Append to existing index.");
 }
 
 
diff --git a/AnnService/src/IndexBuilder/main.cpp b/AnnService/src/IndexBuilder/main.cpp
index ba4de4612..3e6a54edd 100644
--- a/AnnService/src/IndexBuilder/main.cpp
+++ b/AnnService/src/IndexBuilder/main.cpp
@@ -55,7 +55,9 @@ int main(int argc, char* argv[])
         indexBuilder->SetParameter(iter.first.c_str(), iter.second.c_str());
     }
 
-    ErrorCode code;
+    std::shared_ptr<VectorSet> p_vectorSet = nullptr;
+    std::shared_ptr<MetadataSet> p_metaSet = nullptr;
+
     if (options->m_inputFiles.find("BIN:") == 0) {
         std::vector<std::string> files = SPTAG::Helper::StrUtils::SplitString(options->m_inputFiles.substr(4), ",");
         std::ifstream inputStream(files[0], std::ifstream::binary);
@@ -71,14 +73,12 @@ int main(int argc, char* argv[])
         char* vecBuf = reinterpret_cast<char*>(vectorSet.Data());
         inputStream.read(vecBuf, totalRecordVectorBytes);
         inputStream.close();
-        std::shared_ptr<VectorSet> p_vectorSet(new BasicVectorSet(vectorSet, options->m_inputValueType, col, row));
+
+        p_vectorSet.reset(new BasicVectorSet(vectorSet, options->m_inputValueType, col, row));
         
-        std::shared_ptr<MetadataSet> p_metaSet = nullptr;
         if (files.size() >= 3) {
             p_metaSet.reset(new FileMetadataSet(files[1], files[2]));
         }
-        code = indexBuilder->BuildIndex(p_vectorSet, p_metaSet);
-        indexBuilder->SaveIndex(options->m_outputFolder);
     }
     else {
         auto vectorReader = IndexBuilder::VectorSetReader::CreateInstance(options);
@@ -87,9 +87,21 @@ int main(int argc, char* argv[])
             fprintf(stderr, "Failed to read input file.\n");
             exit(1);
         }
-        code = indexBuilder->BuildIndex(vectorReader->GetVectorSet(), vectorReader->GetMetadataSet());
-        indexBuilder->SaveIndex(options->m_outputFolder);
+
+        p_vectorSet = vectorReader->GetVectorSet();
+        p_metaSet = vectorReader->GetMetadataSet();
+    }
+
+    ErrorCode code;
+    std::shared_ptr<SPTAG::VectorIndex> vecIndex;
+    if (options->m_append && ErrorCode::Success == indexBuilder->LoadIndex(options->m_outputFolder, vecIndex) && nullptr != vecIndex) {
+        code = vecIndex->AddIndex(p_vectorSet, p_metaSet);
+        indexBuilder = vecIndex;
+    }
+    else {
+        code = indexBuilder->BuildIndex(p_vectorSet, p_metaSet);
     }
+    indexBuilder->SaveIndex(options->m_outputFolder);
 
     if (ErrorCode::Success != code)
     {
diff --git a/docs/GettingStart.md b/docs/GettingStart.md
index 756aa70ed..1d2dae300 100644
--- a/docs/GettingStart.md
+++ b/docs/GettingStart.md
@@ -11,6 +11,7 @@
   -o, --outputfolder <value>    Output folder, required.
   -a, --algo <value>            Index Algorithm type (e.g. BKT, KDT), required.
 
+  -p, --append <true|false>     Indicate whether the data should be appended to an existing index, if one exists.
   -t, --thread <value>          Thread Number, default is 32.
   --delimiter <value>           Vector delimiter, default is |.
   Index.<ArgName>=<ArgValue>    Set the algorithm parameter ArgName with value ArgValue.