Abstract: The phenomena of changes of astronaut's thermoregulatory functions and inter relations between them caused by the effect of weightlessness in both spaceflight and simulated space environment on the earth are systematically analyzed and summarized.It is pointed out that in weightlessness environment the spontaneous convection disappears ,the body fluid shifts toward head and torso,the body water loses by urinating,the function of cardiovascular system weakens and the maximal oxygen intake reduces.All above will disable thermoregulatory function and finally disturb the heat tolerance of astronauts significantly.Furthermore,within the thermoregulatory mechanism,behavioral regulation acts as a supplement and extension related to the physiological regulation.The former can,however,play a role only on the latter.Thus,in design of the cabin thermal control system and space suit ventilation-liquid-cooling system,the effect of weightlessness should be considered.