Abstract: The pressure vessel internals of high-temperature gas-cooled reactor are composed of graphite and boron carbide sintered ceramic materials. The primary reactor internals need to be heated and dehumidified during the hot state function test. According to the characteristics of the primary loop hot test system of high-temperature gas-cooled reactor, the three-dimensional numerical models of pressure vessel, steam generator and main helium fan are constructed by using COMSOL multi-physics 5.4 calculation software. The reliability of the model is verified by the heating test values of the demonstration project, and the dynamic characteristics of the temperature field during the heating process of the primary loop are obtained. In order to solve the problem of low heating efficiency of the primary circuit in the demonstration project of high-temperature gas-cooled reactor, a method of introducing the auxiliary steam into the steam generator and dynamically adjusting the operating parameters of the auxiliary steam to heat the primary circuit helium is proposed. The results show that compared with the main helium fan heating mode, adding auxiliary steam heat source can save about 31.3 h of heating time, and increase the final equilibrium temperature of the reactor core from 250 ℃ to 265 ℃. On the premise of meeting the operation criteria, it is more conducive to the dehumidification of the carbon brick and graphite reactor internals. The study results provide strong support for the hot test of the primary circuit of the high-temperature gas-cooled reactor.