Generally, formation flying should be taken into consideration during satellite development. Aiming at the demand of precise formation control, a distributed dynamics simulation and test system for formation flying satellites based on EtherCAT is proposed in this article, compared with traditional single satellite dynamics simulation systems. Taking the advantages of EtherCAT’s real-time character, flexible topology and extensibility, the system is capable of integrated dispatching and data management, including the real-time simulation function of satellite data, formation topology and dynamic characteristics. In this paper, the validity has been demonstrated by constructing the EtherCAT based distributed system and designing the integrated dispatching software. Finally, the real-time performance of the proposed system has been tested and verified better than 1 ms, which meets the requirement of satellite formation dynamics simulation and test.