Abstract: With the rapid development of web services，the approach of building available composite web services flexibly and efficiently has become a hot point of research.The lifecycle of service composition is researched.According to the function partition of definition phase，selection phase，construction phase and execution phase，the composite service can be developed flexibly and executed efficiently.With the service availability maintenance phase，the service information of service registry is updated timely，so the availability of the information is improved obviously.As a result，the availability of composite service definition is improved to make sure its successful execution.

Key words: service composition, lifecycle, availability

摘要： 随着Web服务的快速发展及广泛应用，如何灵活高效地建立有效的组合服务已成为研究热点。针对服务组合生命周期的研究，通过定义阶段、选择阶段、构造阶段以及执行阶段等各生命周期阶段的功能划分，实现灵活高效的服务组合；通过有效性维护阶段保持服务注册中心中的服务信息以及组合服务定义的有效性，最终保证组合服务的成功执行。

关键词: 服务组合, 生命周期, 有效性