Abstract: The connecting bolt of electric pump in an offshore oilfield was fractured. The causes of bolt fracture were analyzed by means of macroscopic observation, fracture analysis, chemical composition analysis, hardness test and metallographic examination.The results show that the fracture mode of the bolt was fatigue fracture. During the service process, pitting corrosion occured at the root of the bolt, which in turn induced stress corrosion microcracks. Under the action of the vibration stress of the electric pump, the corrosion microcracks further expanded until the bolt broke.