The performance of fiber optic gyroscope (FOG) exhibits temperature dependence due to nonreciprocity phase shift in the fiber coil induced by environmental temperature variation. Research on temperature characteristic is meaningful for high precision FOG working in harsh environment. In this letter, modeling of thermal-induced rate error for FOG with environmental temperature ranging from to 60 is investigated. Temperature dependence of fiber refractive index, thermal expansion of the fiber, and thermal stress of the fiber coating are all considered in our model. Experiments with different temperature change rates between and 60 are performed to verify the effectiveness of the proposed model. Experimental results show great agreement with theoretical values.