The instability of polarization degree influences the performance of fiber optic gyro in SLD start- up process, which severely restricted the research on quick start of fiber optic gyro. It is analyzed that the polarization characteristics of TE mode, TM mode and influencing factors theoretically, it is concluded that the degree of polarization increases with the increase of drive current and reduces with increase of temperature, a high-speed data acquisition scheme is designed to test the changes of polarization degree, drive current and temperature of chip in SLD start-up process, it has been obtained that the rise time of drive current is about 0.3 s, the stability time of temperature is about 3 s and the polarization degree of SLD is about 4.3%, and the effect of polarization characteristics on polarization error of fiber optic gyro has been analysed when SLD starts up.