The polarization-maintaining fiber coil in a fiber optic gyro (FOG) is a sensitive element, its loss will increase when it works in radiation environment such as the spatial, and the performance of FOG also degracles. The spatial radiation enviroment is simulated with 60Co as the radiation source, and influences of spatial radiation on elements of fiber optic gyro especially the polarization-maintaining fiber, were researched based on lots of simulation experiments of spatial radiation. It is found the polarization-maintaining fiber suffers from the spatial radiation most seriously, and the radiation effect mechanism of polarization-maintaining fiber has been proposed. Furthermore, the radiation effect on fiber opti gyro owing to the increase of loss in polarization-maintaining fiber under radiation has been discussed, which provides theoretical foundation for radiation hardening design of fiber optic gyro.