Based on partial differential equation of heat conduction, a temperature field model of fiber optic gyroscope (FOG) was established. The steady-state temperature field and the transient temperature field were given. A circuit to measure temperature using a platinum resistor was designed. The experiment results are compared with the simulated ones and the error is less than 3%, which validates the legitimacy of the simulation. The structure of FOG was redesigned to improve the thermal symmetry of the fiber ring. The steady-state temperature field indicates that the temperature difference of the fiber ring is reduced 73.7 percent to 0.05 degree after structure redesign. The transient temperature field in 10 min shows that the temperature difference of the fiber ring is reduced 42.1 percent to 0.11 degree after structure redesign. 