According to the polarization coupling model of the polarization-maintaining delay optical fiber coil, considering the reciprocal parasitic waves with large amplitude, the interference intensity of the optical system in the fiber-optic current sensor (FOCS) is calculated, and the theoretical relationship between the scale factor and the polarization crosstalk of the delay fiber coil is obtained. The effect mechanism of the temperature dependence of the polarization crosstalk on the scale factor is revealed, and the corresponding suppression methods are proposed. To ensure the scale factor error to be within 0.2% under the varied temperature condition, it is essential for the polarization crosstalk of the delay fiber coil to be less than -30 dB. The experimental results show that the temperature performance of the FOCS can be improved greatly when lowering the tension of winding fiber, reducing the quantity of the glue, and utilizing the frame with low temperature coefficient. The variation of the scale factor is decreased from 0.63% to 0.07% over the temperature range from -40 ℃ to 70 ℃. The research work offers a theoretical guide for the design and manufacture of the optical fiber delayed coil in the FOCS.