It is not perfect to estimate the reliability of primary mirror supporting structures in space cameras based on the peak value of stress response at a random vibration environment. In accordance with the fracture of supporting structure in a random vibrating test, this paper presents an analysis method of vibration fatigue life to explore the reliability of primary mirror supporting structures, and uses a simulation technology to predict the fatigue lifespan of a supporting structure. Based on the theories of Finite Element Method and random vibration fatigue, the random vibrating fatigue life of the primary mirror supporting structure for a space camera is analyzed by an analysis software. The fatigue lifespan distribution of the whole body and the lifespan values of the most dangerous points are obtained. Experimental results indicate that the simulation results are consistent with the experimental data, which means the proposed method is feasible.