Abstract: The theory and the numerical analysis of the external-heat simulator with infrared heating rod are discussed, together with its applications in the thermal vacuum tests. The computational model of the new external-heat simulator is built to analyze its heating capability and the temperature control effect. Tests are carried out to validate the temperature response characteristics and the heating capability of the simulator. The new simulator can be applied in the spacecraft thermal vacuum test, for its fast temperature response, the large range of the heating rod coverage coefficient and resistance, which improves the flexibility of the heating capacity design.