Based on the principle of ladder wave modulation of digital FOG, a selfcalibration method of scale factor aimed at improving the efficiency of fiber optic gyro calibration was proposed. The equal amplitude increased digital ladder wave signal was added into the digital signal processing section of gyro FPGA.The difference of phase between the two light was changed by Y waveguide. Then the angular velocity of the input of turntable was simulated to fit the scale factor and calculate the nonlinearity error under the static conditions. Test result verified the feasibility of the selfcalibration of fiber optic gyro and its application scope was also studied.