A compensating method for unbalance torque resulted from the platform deforming of the air-bearing spacecraft simulator acted on gravity is presented, that is making a tiny distance between the mass-center and the center of rotation of the platform in the vertical direction so as to offset the unbalance torque resulted from the shift the mass-center with respect to the center of rotation of the platform and from the platform deforming when acted on gravity in the maximum work range of two horizontal Eulerian angle. The change trend of maximum unbalance torque after compensated is discussed by the theory on spacecraft altitude kinetics. It is demonstrated that this method can be applied to any case that the air-bearing spacecraft simulator rotate around the horizontal axis. The result shows the maximum unbalance torque after compensated is only 1/25 little than the one before compensated.