The gyroscope drift is the main error resource of the inertial stabilized platform. Calibrating and compensating the gyroscope drift is the key to improving the performance of the platform. Because the off-line test results cannot properly illustrate the characteristics of the on-line gyroscopes, calibrating the gyroscope drift in the platform system is necessary. In the geometrical stability state, only the drift affects the platform movement, and the movement can be described with the differential equations. Based on these differential equations, the authors built a set of system state equations, with the drift model coefficients as the state variables. By using the outputs of the accelerometers on the platform as the measurement values, an extended Kalman filter can estimate the drift model coefficients of gyroscopes. The effectiveness and precision of the new test method was evaluated through the simulation.