For Web applications,component-based software development is also a way to improve the efficiency of development,whose solution involves the combination of the front-end and the back-end or third-party services.We proposed a component composition technology based on AJAX for Web application,based on the analysis on the component types and its composition pattern of the Web application.In this technology,we proposed two different solutions for combination of different component types.One uses jQuery to invoke Servlet while the other uses DWR technology to enable interaction between front-end page component and back-end business component or Web Service component.In addition,based on the proposed method,this paper implemented two online Web application component composition tools through two implementation styles,which allow users to define the composition details through graphical user interface and automatically complete the component composition process to generate Web applications.This paper used an experimental course selection website as an application development example,to verify the usefulness of the technology and the tool.