Abstract: In order to study the heat transfer performance of the spray cooling system under negative pressure environment, a set of closed spray cooling system with water as the working medium was built. The heat flux, heat transfer coefficient, and temperature of the cooling surface, which characterize the heat transfer capability of the system under different pressures, were calculated and tested. The results show that, when the spray flow rate is 0.45 L/min, both heat flux and heat transfer coefficient increase with the decrease of the pressure in the spray chamber. When the pressure in chamber drops to 20 kPa, the heat transfer coefficient increases by 95.2% compared with that at atmospheric pressure. However, when the spray flow rate comes to 0.25 L/min, both heat flux and heat transfer coefficient first increase and then decrease with the decrease of the pressure in the spray chamber. As the heating power increases from 100 W to 1200 W, both heat flux and heat transfer coefficient increase significantly with the decrease of chamber pressure, whereas the applicable thermal conditions gradually narrow down. The surface temperature uniformity in low-pressure environments is worse than that in atmospheric environments. The proposed research may provide a reference for the application of spray cooling technology on spacecraft.