This study investigates the thermal effects on the deformation of herringbone gear teeth and the gear body, and presents the mathematical representation of thermal deformation of body and tooth profile. Subsequently, an analytical model of gear mesh stiffness that incorporates the temperature effect is developed based on the tooth root transition curve equation, the potential energy method, and the slice integration principle. The accuracy of this model is then validated through the application of the finite element method. Furthermore, the influence of friction coefficient, speed, and torque operating parameters on mesh stiffness is analyzed through the presented model. Results show that, under thermal effect, both the meshing stiffness of a single pair of teeth and comprehensive meshing stiffness of the gear increase by about 9%. Moreover, the mesh stiffness increases with the increase of friction coefficient, rotational speed, and torque, among which the torque has the greatest influence on the meshing stiffness.