According to the IM system's functional requirements, completed the overall design of IM system server, which has good function of communication and plug-in management. Propose the user login server optimized design, build a complete user login process, and design custom protocol packet structure. As well as design and implement the optimization methods of login server by using software. Finally, verify the feasibility and reliability of the system in a lab network environment, so as to provide a stable system server when the number of users will growth continually in future.