At present, the construction of the new smart city management platform based on CIM is still in initial stage. According to the characteristics of this platform, this paper puts forward the scalability of software integration that should be considered in the top-level design of the platform. By analyzing the characteristics and the requirements of the platform, as well as analyzing the design method of extensibility structure, this paper puts forwards the design of extensibility architecture and the method of platform development mode selection based on extensibility requirements, so as to achieve the purpose of improving the service capability of integration and avoiding the waste of human and financial resources caused by the reconstruction of the platform.