Abstract: During the wheel radial fatigue test,several high strength bolts fractured in different degrees. Through the fatigue fracture mechanism and macro inspection, chemical composition analysis, mechanical property test, metallographic examination and other methods,the causes of bolt fracture are analyzed. It is found that crystal inclusions,improper heat treatment and inadequate pre-tightening force of bolt installation cause the strength and fatigue of some areas on the bolt surface decrease,and stress cracks appear,which will lead to fatigue fracture failure.