With the development and improvement of Session Initiation Protocol (SIP), servers based on SIP have been widely applied in Communication Systems. However, the performance of single SIP server to handle SIP messages is limited on the condition of the hardware does not upgrade. The performance won't meet the demand of large-scale increasing of the number of users. Through of research and analysis on SIP, the paper designed and implemented SIP Server Clusters. By using multiple servers working together, more requests can be dealt with concurrently, which is an improvement of performance. The design is simple to implement and has high scalability. These clusters Practice has proved that the proposed solution can adequately address the current shortage, providing supports for future services expansion.