According to the error parameters of fiber optic gyro are not stable and vary with time slowly in two-axis indexing rotary strapdown inertial navigation system, a novel calibration method was proposed in this paper. The calibration method can be carried out based on the angle between the IMU and the body could be calculated. Combine with the error model of IFOG. The eight position calibration method was proposed and the parameters of FOG could be calculated. Coupling errors between the scale factor and the misalignment can be avoided by this method. Turntable experiment results show that, the calibration method would achieve the high accuracy with the attitude of vehicle uncertainty.