Abstract: A study of system simulation of satellite constellation is introduced. System simulation would play an important role in Computer Aided Design (CAD) of satellite constellation. From the point of view of orbital dynamics, the concept and requirements of system simulation of constellation are presented, the mathematical models for system simulation are established, the hierarchy and architecture of software implementation are studied. At last, a program accomplished by the authors for system simulation of constellation is briefly introduced. Simulation results show that the system simulation software are beneficial to optimization of constellation design, verification of constellation control strategies, etc.