In order to study the temperature performance of polarization maintaining fiber coil which is used in middling or high precision fiber optic gyroscope (FOG),the main reasons affecting the performance of fiber coil are analyzed from the viewpoint of the manufacturing process and the temperature changes of external environment. The light wave signal’s polarization cross-coupling of the interferometer is qualitative analyzed by using coupled wave idea,and the major polarization errors which affect the performance of FOG are pointed out. According to the transient state of temperature effects of fiber coil,the temperature test system is established to study the signal polarization’s changes in fiber coil. Experimental results show that the polarization state of the optical signals is affected by temperature in fiber coil,and also is concerned with temperature distribute of the whole fiber coil. In addition,this system can be used as the performance evaluation system to filter fiber coils with outstanding performance.