Threshold stress intensity factor KIH would be an appropriate index parameter for the cut-off limit in fatigue crack growth analysis in order to prevent hydrogen storage tanks from suffering brittle fractures at hydrogen stations. The KIH factors were evaluated using rising load and constant displacement tests conducted in high-pressure gaseous hydrogen. The following results were obtained: 1. KIH measured under rising load was less than KIH measured under constant displacement. 2. The difference of KIH increased as tensile strength decreased. 3. The difference of KIH may be attributed to the plastic wake of propagating cracks. Hydrogen diffusion behavior at crack tips was also estimated by a finite difference method analysis.