Abstract: The infrared lamp array is usually used for simulating the external thermal flux in the test of spacecraft and solar array. A model is set up in this paper to calculate the flux uniformity on the spacecraft surface where the infrared lamp array is used for the flux simulation. Factors that affect the flux uniformity of a planar infrared lamp array are analyzed, and some methods of optimizing the design are proposed to improve the flux uniformity on the spacecraft surface. Those methods can provide guidance for the design of the infrared heating cage used in spacecraft vacuum thermal tests.