In this paper, the aerospace SEP(Single Event Phenomenon) fault injection system based on inserting fault both in the memory and through the bus is presented. The structure and functions of FIS(fault injection system) are firstly introduced. On the basis of expansibility and universality, the study is concentrated on the key implementation technology in fault insertion unit. The practical results show that the FIS is low cost, high universality, fully dynadrically and real-timely inserted.