Abstract: Failure analysis on a 30CrMnSiNi2A steel bolt used for a wing cover plate which fractured huring storage after assembly was carried out by macro and micro observation of the fracture surface,microstructure inspection and hydrogen content test.The improvement measure was introduced.The results show that the failure mode of the bolt was hydrogen brittle fracture.The reason of hydrogen brittle fracture was the over-high material strength and hydrogen content.Decreasing the strength of the bolt to a proper level was a valid measure to prevent and control hydrogen brittle fracture of the high strength bolts based on the standard dehydrogenation process.