Abstract: During the maintenance of a certain equipment, it was found that the elastic cylindrical pin of 65Mn spring steel in the equipment was cracked and failed. The failure causes of the cylindrical pin were analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination, fracture analysis and hydrogen mass fraction determination. The results show that there was no corresponding dehydrogenation process after back plating process, and hydrogen element penetrated into the cylindrical pin, which led to hydrogen embrittlement failure of the elastic cylindrical pin.