In view of the problem of the location of indoor wall condensation, simulates numerically the indoor natural convection under the action of thermal Rayleigh numbers and moisture Rayleigh numbers by the the method of computional fluid dynamics(CFD), and analyses the indoor air relative humidity distribution and determines the indoor possible condensation areas. The results indicate that the indoor air flow strengthens when the temperature gradient and the water vapor mass fraction gradient are in the same direction, otherwise it decreases. The indoor air flow structure directly affects the indoor relative humidity, and the point of maximum relative humidity locates at the wall of high moisture fraction, which moves along the flow direction with the increased flow intensity.