Nuclear batteries were widely used in space exploration, nuclear industry and other fields. Because of the particularity of nuclear battery structure and materials, methods based on equivalent thermal power were often used when measuring their power. At present, the thermal power standard device used for measuring the nuclear battery thermal power measurement device in our country had the problems of low accuracy and poor stability. In order to solve the problems, this paper developed a set of standard heat source device. It consisted of a high-precision constant current source, a standard resistance, a standard heat source, an eight-and-a-half-digit digital multimeter, etc., which was based on the Joule effect of current and the principle of converting electrical energy into heat energy. It had been verified by experiments that in the range of current less than 3A, 0.7~147 W of power can be generated, and the relative expanded uncertainty was equal or less than 2×10-3 (k=2). It played an important role in ensuring the accurate traceability of the thermal power of nuclear batteries.