Abstract: Comprehensive analysis was carried on by means of macro analysis and chemical composition analysis, metallographic examination, mechanical properties testing to analysis the failure mechanism of 25Cr2MoVA locating bolts.The results show that morphology of the fracture was typical fatigue failure.the hardness of the fractured position was higher than requirements and the impact energy is well below the requirements.The microstructure is tempered.orga-nization has a certain direction,the ball is not complete.This is closely related to its improper heat treatment,it can not meet its operational performance requirements

Key words: positioning, bolt, fatigue fracture