Abstract: A 17-4PH steel bolt broke during use in the marine environment. The cause of bolt fracture was analyzed using macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy analysis. The results show that the aging temperature of the bolt was too low during the heat treatment process, resulted in the appearance of more martensite in the material and the generation of significant tissue stress. Under the action of H ions, the bolt ultimately underwent hydrogen embrittlement fracture.