diff --git a/README.md b/README.md
index 0853778f..221829b5 100644
--- a/README.md
+++ b/README.md
@@ -252,6 +252,8 @@ const password = 'your-milvus-password'; // optional password
 
 // connect to milvus
 const client = new MilvusClient({ address, username, password });
+// wait until connecting finished
+await client.connectPromise;
 ```
 
 ### Create a collection
diff --git a/milvus/grpc/GrpcClient.ts b/milvus/grpc/GrpcClient.ts
index d494506f..688efcfc 100644
--- a/milvus/grpc/GrpcClient.ts
+++ b/milvus/grpc/GrpcClient.ts
@@ -244,6 +244,8 @@ export class GRPCClient extends User {
    * This method returns a Promise that resolves with a `GetVersionResponse` object.
    */
   async getVersion(): Promise<GetVersionResponse> {
+    // wait until connecting finished
+    await this.connectPromise;
     return await promisify(this.channelPool, 'GetVersion', {}, this.timeout);
   }
 
@@ -252,6 +254,8 @@ export class GRPCClient extends User {
    * This method returns a Promise that resolves with a `CheckHealthResponse` object.
    */
   async checkHealth(): Promise<CheckHealthResponse> {
+    // wait until connecting finished
+    await this.connectPromise;
     return await promisify(this.channelPool, 'CheckHealth', {}, this.timeout);
   }
 }
diff --git a/test/grpc/MilvusClient.spec.ts b/test/grpc/MilvusClient.spec.ts
index ff4b6767..d09117ab 100644
--- a/test/grpc/MilvusClient.spec.ts
+++ b/test/grpc/MilvusClient.spec.ts
@@ -194,6 +194,14 @@ describe(`Milvus client`, () => {
     expect(Array.isArray(res.reasons)).toBe(true);
   });
 
+  it(`Should throw when server is unavailable`, async () => {
+    const m10 = new MilvusClient({ address: IP.replace(':19530', ':19539') });
+    await expect(m10.connectPromise).rejects.toThrow('UNAVAILABLE');
+    await expect(m10.getVersion()).rejects.toThrow('UNAVAILABLE');
+    await expect(m10.checkCompatibility()).rejects.toThrow('UNAVAILABLE');
+    await expect(m10.checkHealth()).rejects.toThrow('UNAVAILABLE');
+  });
+
   it(`Expect close connection success`, async () => {
     expect(milvusClient.channelPool.size).toBeGreaterThan(0);