A method of determining fatigue of a pressure-resistant component for high-pressure hydrogen made of a ferritic steel and provided in a high-pressure hydrogen gas environment is provided wherein when the material of the ferritic steel in the air has an ultimate tensile strength Su in the range of 958-1,144 MPa and the hydrogen gas environment has a pressure in a range to 45 MPa, then a fatigue strength in a gaseous hydrogen SH (MPa) for the pressure-resistant component provided in the high-pressure hydrogen gas environment is obtained by using equation (1): SH (MPa)=2,577−1.8925×Su (MPa). The influence of a high-pressure hydrogen gas environment on the pressure-resistant component for high-pressure hydrogen is determined based on the fatigue strength obtained by using the equation (1).