This article designed a communication simulation system for spacecraft system network which consist of mullti groups of 1553B bus and RS422 bus. By hybrid programming of C language and CVI, the simulation system simulates the collection, handling, displaying and storage of data from telemetric and command with multithreading mechanism. And the system has the characteristics of friendly man-machine interface, high real-time, high reliability and low cost. Test results showed that the system functions and performance completely meet the simulation requirement of spacecraft system network. The simulation system gives a strong support for system network design of the spacecraft and shortens the research and development cycle.