This work provides a numerical analysis method for on a scale of several tuns to a hundred micrometers Solid Oxide Fuel Cells phenomena. The analysis depends on the assumption that the effective electrode reaction area is restricted to the three phase boundary where mass fluxes and electric current are concentrated and cause polarization, Concentration profiles were detailed analytically. and used for calculating polarization and voltage-current curves. Optimum calculations for cathode structure showed that the composite particle diameter electrode gives better SOFC performance.