Abstract: The design and simulation of the medium scale space environment simulator for the extravehicular activity space suit experiment were discussed.By simulating the temperature of the cryopanel and the relation between the pressure and pumping gas speed of the cryopump,it was verified the vacuum system design was rational.The pre-cooling of the medium scale space environment simulator adopted the open liquid nitrogen system in order to simplify system structure.The structure analysis and the radiation heat load computation were carried out from the cryopanel to the radiation baffle.The effects of the condensing layer of the cryopanel on the cryopump capabilities were analyzed.By simulating cryopanel temperature field and analyzing the maximum of temperature,the cryopanel design was optimized and the capabilities were verified.The oxygen wastage of the astronaut was analyzed to estimate the metabolism producing heat of the astronaut.The medium scale space environment simulator heat loads and the liquid helium demand of the cryopump were obtained.The system design and simulation of the medium scale space environment simulator provides the reference for the research of domestic astronaut extravehicular activity and correlative devices.