Abstract: In vacuum thermal tests, the cylindrical infrared heating cage is usually selected for simulating the thermal flux on the cylindrical spacecraft surface. The distribution of flux on spacecraft surface is simulated with a cylindrical infrared heating cage in this paper for different parameters, including the cover coefficient of infrared heating cage, distance between infrared heating cage and spacecraft surface, and the size of the marginal region. The method of optimization design for the cylindrical infrared heating cage is used to improve the flux uniformity on the spacecraft surface in simulation.