Abstract: Being an advanced technique of spacecraft system,the distributed satellite has become one of the research hotpots.According to the running environment and the tasks of distributed satellite,and considering its reliability,security,and real-time requirements,a design method of master-assistant dual-system architecture based on three-level fault-tolerance was presented.The properties and design requirements of distributed satellite were discussed.And the designs of three-level fault-tolerance,security mechanism of master-assistant dual-system,and assistant system based on trusted platform module (TPM) were introduced.The design method has been tested in a prototype system.It showed that the system effectively resolved the reliability,security,and real-time problems of the distributed satellite.