Presently, there are a significant number of investigations that study the influences of the hydrogen embrittlement on pressure vessels for hydrogen storage. But few of them consider the effects of helium-3 decayed from hydrogen. This paper studies the effects of the high-pressure hydrogen on mechanical behavior of a kind of steel pressure vessel by elastic-plastic finite element simulations, based on the explosion tests data of 4-, 6-, 14- and 17-year hydrogen storage vessels and relating experimental data of materials properties. Then the mechanical responses of the 50-year hydrogen storage pressure vessel are predicted. The results provide guidelines for design and evaluating hydrogen storage vessels.