The growth rate of fatigue cracks is accelerated under high pressure hydrogen because of hydrogen embrittlement. Hydrogen diffusion is enhanced by a hydrostatic stress field, and an accumulation of hydrogen in the fracture point is necessary to cause hydrogen embrittlement. In this paper, fatigue crack growth behavior under different hydrogen pressure was first investigated. Hydrogen diffusion behavior was analyzed by a finite element analysis based on the Fick’s diffusion theory with a modification in the stress gradient term. Fatigue crack growth rate was accelerated by higher pressure because of increased hydrogen concentration around the crack tip region. Clear relationship was...