The finite element model of double involute gears was established,the effect of tooth surface friction force on contact stress was analyzed,and the analysis result was compared with that of involute gear.The results show that the maximum equivalent contact stress between the double involute gears and the involute gear has little difference,while the distribution of contact stress is different under the same friction condition.The high contact stress is near the node for the involute gear and near the root for the double involute gear.The tooth surface friction force has little influence on the distribution of contact stress,and large influence on the numerical value of contact stress.Therefore,the effect of tooth surface friction force must be considered in the analysis of contact stress.It is an effective method to improve the anti pitting ability and the contact fatigue life of gear by changing the lubrication condition of the tooth surface to reduce the tooth surface friction.