With the new application systems integrated with existing systems, many problems have arisen, such as system integration difficultly and audit function loss. Hence, Single Sign-on has become an important solution for popular enterprise business integration at present. According to the research and exploration of SSO system which is based on YaleCAS authentication protocol, this paper introduced the integration of application systems using user-mapping with making the least amount of modifications. In addition, this paper has provided a complete security audit function for the single sign-on system, so a more comprehensive system security can be provided.