The commercially supplied pure iron was cathodically hydrogen charged at various current densities in sulfuric acid aqueous solution in order to investigate the blister growth behavior, and the computer simulation was carried out to predict the blister formation characteristics. The relationship between maximum blister diameter observed on the specimen surface dm(mm), hydrogen charging current density ic(A/m3), and charging time tc(ks) was expressable as: dm=3.6×10-3i0.61ct0.61c. By means of the computer simulation obtained by assuming random walk of hydrogen in metal, the relation, dm=5.1×10-3i0.56ct0.63c, was obtained; this relation could predict well the blister diameter experimentally obtained. Moreover, the simulation could display the three-dimensional distribution of blisters inside the specimen.