A platform in orbit calibrating method, in particular a six-degree-of-freedom Gough-Stewart platform -on-orbit calibration method, by compensating the actuator force coefficients of the active pointing superstatic platform, the three-axis attitude coupling coefficients of the actuator loads of the active pointing superstatic platform are reduced. The method comprises the following steps: determining the resultant moment normalized result actually received by the three axes of the center of mass of the load as a whole according to the three axes attitude and the three axes principal inertia ofthe load as a whole normalized; According to the translational displacement of the normalized load center of mass, the actual triaxial force acting on the load center of mass is normalized. Accordingto the translational displacement of the normalized load center of mass and the actual triaxial force of the normalized load center of mass, the optimal solution of the actuator force coefficient is obtained by iterative calculation. According to the identified actuator force coefficients, the driving current of the active pointing superstatic actuator is compensated, and the three-axis attitude decoupling of the active pointing superstatic platform is realized, and the three-axis attitude coupling coefficients are reduced.