The three-dimensional method is described for treating U-Pb isotopic data obeying a two-stage evolution. The U-Pb discordia plane model and the Pb-Pb isochron plane model are developed respectively, to eliminate the effect of the unknown common lead correction. Calculation formulae of best-fit plane parameters are given and some examples from the literature are recalculated to demonstrate the applicability of the method. The plane-fitting can be a convenient means in U-Pb dating.