Bending fretting fatigue tests of 40CrNi2MoA alloy steel were carried out under different bending loads,and its bending fretting fatigue stress curve was built up.Through the micro analyses of fretting damage zones,the bending fretting fatigue damage characteristics of the alloy steel were investigated.The results show that the bending fretting fatigue stress curve of 40CrNi2MoA steel with a shape of “C” is quite different from the plain fatigue stress curve.With the increase of the bending fatigue load,the fretting runs in the partial slip regime (PSR),mixed regime (MR),and slip regime (SR),respectively.Different from the other two regimes,the cracks are easier to initiate and propagate in the mixed regime,and the fretting fatigue life is the lowest.The wear mechanisms of sample surface mainly are abrasive wear,oxidative wear and delamination.According to the different influence of contact stress and bending stress,the crack propagation of bending fretting fatigue can be divided into three stages,which are respectively controlled by the contact stress,the coupling of contact stress and bending stress,only the bending stress.