An improved approach for orthogonal compensation is proposed to solve the problem of traditional method that has difficulty in satisfying relatively higher orthogonal compensation precision of inertial measurement unit（IMU）.The installation error equations of both three axis accelerometers and three axis fiber-optic gyro sensors are formulated

respectively.Then rate calibration and multi-position static calibration of IMU are conducted

compute installation error equation parameters of IMU by means of least square algorithm.Both simulated and experimental results show that the proposed orthogonal compensation approach has higher precision in terms of both orthogonal compensation and sensor calibration

as compared with the conventional orthogonal compensation one.Furthermore

the proposed method also solves the problem of calculating the IMU zero bias by using indexing mechanism during static calibration

and thus the calibration efficiency of IMU can be greatly improved.