Abstract: To estimate the capability of air forced convention heat transfer in thermal control of large manned spacecraft,the principle of air flow parameters and physical properties varying with the dropping pressure was studied.The relationship between the atmosphere pressure and the coefficient of air forced convection heat transfer in the empirical and practical relations was pressented,and a numerical example was provided to prove this relationship.The results indicate the heat transfer capability of air forced convection decreased with the atmosphere pressure in the cabin of manned spacecraft dropping,and the air forced convection contributed little to the equipment heat dissipation when the pressure was lower than 3.04×104Pa.