Abstract: The natural convection results of the heat transfer and the temperature distribution under the on-orbit condition in the manned spacecraft pressured cabin would be different from those obtained during the terrestrial test. A numerical model for the manned spacecraft pressured cabin is built and solved by the simulation software. The results including the 1g and 0g states are compared with respect to the air flow and the heat transfer. It is shown that the gravity has a significant effect on the heat transfer of the wall. and liale effect on the air temperature. The effect of the gravity becomes more significant with the increase of the temperature difference between the air and the wall. The air flow enhancement and the ventilation between cabins impair the effect ofthe gravity. A correction must be made for the heat transfer ofthe wall during the terrestrial test in a gravity field.