Abstract: The kinetics of electrolytic hydrogen evolution reactions ( H.E.R. ) on FCCmetals is considered in terms of statistical mechanics, assuming that the processes obey the catalytic mechanism. Amethod is proposed to calculate the inter-repulsed potentials between the hydrogen atoms adsorbed on crystal surfaces,and the theoretical η-lg(i) curves for H.E.R. on Ni, Pi, Ag, Cu, Au, and Pd arc plotted, respectively.The results show that the theoretical Tafel slope ( ?η/ ?lg(i) = b ) is determined by inter-repulsion between the adsorbed hydrogen atoms, and the intercept a is dependent on the atomic radius and lattice array of metal, and heat of adsorption of hydrogen, etc.