Abstract: In the context of the propulsion system in spacecraft, the helium flow mode in the gas loop, the helium Joule-Thomson effect and its influence on the temperature in the throttle valve are discussed. It is shown that the temperature rise of the helium is about 65 K to 68 K after passing through the value under the normal operating temperature and the pressure range of the gas-loop for spacecraft, and the rise enhances with the increase of the pressure difference between inlet and outlet. The variation of the valve temperature caused by the helium temperature change would lead to some special characteristics of the temperature, as the basis of the thermal control design of the valve.