Thermal battery usually has two types of activation： no-load activation and on-load activation. At present， the thermal battery with load activation is a common activation mode in flight test. The internal resistance changes rapidly from large to small in a short time when it is activated.and the effect of this change on the system power supply has not been reported.. This paper introduces the basic characteristics and working principle of the thermal battery， focusing on the activation mechanism and the possible impact on the system power supply. The resulting problems of system power supply in the test are analyzed and summarized， and several referenceable solutions are provided， which are simple， effective and easy to implement in engineering.