Abstract: The finite difference method is used to calculate the multi dimensional diffusion of hydrogen isotopes in materials. As an example, the two dimenaionl diffusion is numerically analyzed in detail by the alternative directional implicit (ADI) difference method. The distribution of deuterium in stainless steel cylinder once loaded with deuterium is calculated using the finite difference method and the analytic solution of “product” method, respectively, and results are in a good agreement. The multi dimensional diffusion problem can be simplified to some one dimensional ones in either numerical or analytic method.