Abstract: In order to study the optimization method for transient heat flux simulation with infrared heating cage in the thermal vacuum test of spacecraft, this paper establishes a radiation heat transfer model between the spacecraft surface, the infrared heating cage and the heat sink, and obtains the transient temperatures of the cabin plate and the infrared cage, the expression of the arrived heat flux to the spacecraft surface, as well as the relationship between the external heat flux, the internal equivalent absorbed heat flux and the strip current. The equivalent heat absorption inside the spacecraft wall is analyzed. When the control period of the infrared cage is 1 minute, the strip's thermal capacity and the power supply of the infrared heating cage are studied, then the power supply with varied current is optimized. The analysis results can provide a reference for using the infrared heating cage as a transient external heat flux simulation approach to reduce the simulation error.