In order to study the changes of human sweating under simulated weightlessness，the -6° Head-Down Bed Rest (HDBR) experiment usually employed in the researches of Space Medicine and the traditional experiment of human thermal comfort were carried out.During the experiment，micro current of skin，which was presumed as an indicator of human sweating，was measured on 6 male subjects under different air temperatures and relative humidity.The results showed that higher air temperature was required under lower air humidity for sweating after HDBR，and the sweat rate was found to be lower than that before HDBR.In addition，the sweat rate，indicated by skin micro current，increased with the air temperatures under neutral air humidity，but it was significantly less than that before HDBR.Furthermore，the sweat rate of the subjects after HDBR was found to increase rapidly when the air temperature was higher than 29℃ under high air humidity (80%)，and its value was approaching that before HDBR.Moreover，attenuated sensitivity of sweating was observed among the subjects during HDBR，and the sweat rate at the forehead，thorax and back was more significant than those at the lower body and forearm.The results suggest that the human sweating under simulated weightlessness is different from that under terrestrial condition，which can provide evidences for the improvements of the thermal environment during the manned spaceflight.