A method and system for expanding a WebApp application function. The method comprises: adding a function expansion field which contains an expansion JS function and an address of a local application which responds to a request of the expansion JS function in the WebApp; sending each parameter of the function to a browser kernel by calling the expansion JS function; a WebApp frame setting an address of a local application program as the address of the local application which responds to the request of the expansion JS function according to a calling message received by the browser kernel; activating a target application program specified by the address according to the address of the local application; the activated target application program executing the expansion JS function according to the parameters of the expansion JS function and returning an execution result to the WebApp.