To solve the problems that the prelaunch calibration accuracy of ballistic missile is seriously influenced by external disturbance, especially the temperature stability of Fiber Optic Gyro (FOG) is so low that the parameters are changed by temperature influence and the error compensation is not satisfying, a rotating inertial measurement unit based on FOG for the missile is proposed. A rotating axis is added to the strapdown Inertial Measurement Unit (IMU), the IMU rotates around the axis, and the residual error after prelaunch compensation is modulated into periodic terms. Then, error autocompensation is realized. Through theoretical analysis and simulation, not only the constant error and part of misalignment errors of inertial instruments orthogonal to rotating axis, but the first-order, second-order and part of cross-coupling error of intersecting axis of Accelerometers can be compensated by rotating, and the coupling error between rotating speed and error of scale factor and misalignment of FOG can be eliminated completely by selecting appropriate rotating scheme.