Abstract: Various hydrogen trapping sites exist in the steel which can dissolve the hydrogen and decrease the diffusing hydrogen.To investigate the effect of trapping sites on the hydrogen distribution,hydrogen diffusion models and the equilibrium states between the lattice interstitial sites and the hydrogen trapping sites were analyzed by using the theory of gas diffusing in the metal.Hydrogen concentration changing rate with respect to time is equate to the changing rate of hydrogen diffusing from lattice interstitial sites to trapping sites subtract the changing rate of hydrogen desorption from trapping sites to lattice interstitial sites,and the mathematic equation is agreed with McNabb and Foster's hydrogen trapping models.There is local hydrogen equilibrium between the lattice interstitial sites and trapping sites.When the hydrogen occupancy of trapping sites is very low(θ_T ≤ 1),hydrogen effective diffusion coefficient(D_eff) is function of temperature(T) with respect to trapping energy(E_B).