Abstract: The effect of MnS inclusions on hydrogen diffusion in steel was investigated by experiment and finite element method (FEM). The results show that with increasing MnS inclusion content the appearance diffusivity of hydrogen in steel increases when the elongated inclusions parallel to the direction of permeation and decreases when perpendicular to the direction of permeation. If the inclusions can both transport and trap hydrogen, the effect of inclusion on hydrogen diffusion in steel is determined by their strength of transportation and trap, density, figure and orientation.