Abstract: Space radiation heat transfer and heat flux through extravehicular spacesuit must be solved for the design of the spacesuit passive thermal protection. Characteristic of space heat exchange and performance of the vacuum shielding thermal insulation layer for the extravehicular spacesuit were analyzed, four typical position relations among spacesuit, earth, airship, and the solar direction were given, space external radiation heat flow of the spacesuit was analyzed under each of the four conditions, a method of calculating the space heat flux was established, then the maximum calculated heat gain and the maximum heat loss were solved. The final computation results indicate that the capability of the passive thermal protection for the spacesuit has immense influence on space heat flux. The spacesuit thermal insulation is most important to reduce the heat flux, and the ratio of the spacesuit surface solar absorptivity to emissivity should be properly reduced for fear of larger leakage heat flow from the spacesuit.