To improve the accuracy of Strapdown Inertial Navigation System (SINS) based on fiber optic gyro (FOG),the errors of Inertial Measurement Unit (IMU) must be calibrated in laboratory through precise turntable and compensated in SINS.However,the error coefficients of IMU are not stable and vary with time slowly,which degrades the SINS severely in application.To solve the problem,a novel field calibration method is proposed in this paper.The FOG-IMU was rotated 12 times in six-position,and 48 non-linear equations were established according to the error model of FOG-IMU.The non-linear components in these equations were eliminated through the FOG-IMU rotation and the symmetrical position.Therefore,these non-linear equations were transferred to linear equations.Then the error coefficients were calculated by solving these linear equations.Finally,the experiment was carried out,and the experiment results indicate that the novel calibration method can accurately determine 15 error coefficients of FOG-IMU,and the accuracy of this method is equivalent to the classical calibration with the precise turntable.