By constant stress tensile test, the corrosion mechanism of high temperature QPQ treated 25CrMnMo steel specimen in H2S environment was analyzed and discussed. The γ′-Fe4N in the ε compound layer turns into corrosion substance in the test and expands. At the surface of the ε compound layer, the corrosion layer is visible. The compound layer breaks off in little blocks for volume expansion of the corrosion substance and the exterior tensile stress. The coefficient of diffusion of hydrogen atom in the ε compound layer is very low, that decrease the probability of the hydrogen-induced corrosion of high temperature QPQ treated specimens in H2S environment.