Abstract: In vacuum thermal tests，conical infrared heating cages are usually selected for simulating the thermal flux onto conical spacecraft surfaces. The distribution of flux on the spacecraft surface through the conical infrared heating cage is simulated numerically at various parallel distances between the cage and the spacecraft surface, and at various taper angles of the cage. The method of improving the flux uniformity on the spacecraft surface is suggested based on the simulation, which may provide some guidance for the optimal design of infrared heating cage in vacuum thermal tests.