Due to the low speed and heavy load, severe heat and gear contact fatigue failure become serious problems for shield main reducer.The meshing process of a planetary reducer was discretized into 20 meshing attitudes. Through simulation analysis of the thermalmechanical coupling finite element model of the gear, the influence of temperature field on the dynamic meshing contact of gears was studied.Based on the modified S-N curve, each engaging attitude was regarded as a time step, andcontact fatigue life with and without consideration of gear temperature effects was estimated using nCodeDesignLife.The results show that when the gears are in contact, the thermalmechanical coupling contact stress is generally greater than the non-thermal-mechanical coupling contact stress, and the two calculations are generally similar;the thermalmechanical coupling contact fatigue life of the low speed planetary gear is 0.74 times of the normal contact life,the gear temperature rise greatly reduces the contact fatigue life of the gear.