The delay response characteristics of bias drift caused by the non-reciprocity phase errors of a fiber coil in the fiber optic gyroscope (FOG) are investigated. The correlation between temperature and delay time is revealed and the modified temperature drift compensation model is established. In addition, the high-precision FOG experimental system is built. The delay characteristics of the non-reciprocity phase errors are verified using the approximate "square wave" temperature variation at different temperature ranges, and the model parameters of the experimental fiber coil are obtained as well. The test of FOG bias drift in full-temperature is carried out. The experimental results show that the modified model can used to achieve a better compensation effect based on the thermal diffusion mechanism, and the correctness and validity of the new model are verified.