Abstract: As the key component of heat pipe cooling reactor, heat pipe has the advantages of high heat transfer efficiency and excellent isothermal performance. The high working temperature of alkali metal high temperature heat pipe has broad application prospects in the thermal protection of hypersonic vehicle, space nuclear reactor cooling, solar energy utilization and so on. At the same time, the high temperature heat pipe can also be applied to the radiation heat dissipation system of space nuclear power system, the main cooling mode of nuclear powered unmanned underwater vehicle and the waste heat removal device of advanced reactor system. It is the best choice with high heat transfer efficiency and high safety, and can effectively meet the heat dissipation requirements of the nuclear power system of future military and civil equipment systems, overcome the shortcomings of complex structure and insufficient passive safety of traditional nuclear power system. In a word, as a kind of heat transfer device with high thermal conductivity, the core part of heat pipe lies in the evaporation and condensation of its internal working fluid. If there is non-condensable gas in the gas cavity during the working process of the heat pipe, the steam and non-condensable gas in the main flow area will move to the gas-liquid interface together under the action of convective motion. The existence of non-condensable gas hinders the normal condensation of the working fluid at the gas-liquid interface, shortens the effective length of the heat pipe, and breaks the isothermal property of the heat pipe. The area where the non-condensable gas accumulates is called the “inactive” area and has poor thermal conductivity. Therefore, in order to accelerate the in-stack application of high temperature heat pipes, the degree of influence of non-condensable gas on the heat transfer characteristics of high temperature heat pipes is a major problem which is urgent to be settled and evaluated. In this paper, a non-condensable gas area heat transfer model was added based on the thermal resistance network method, and the effect of non-condensable gas on the steady-state heat transfer characteristics of high temperature lithium heat pipes was studied. The results show that with the increase of the volume fraction of non-condensable gas, the temperature of non-condensable gas area decreases more greatly; with the increase of the input power of the evaporation section of the heat pipe, the higher the overall temperature of the normal working area of the heat pipe, the smaller the volume fraction of the same mass of non-condensable gas, and the position where the temperature gradient of the heat pipe wall decreases obviously moves downstream with the increase of power.