The molecular weight distribution functions of the reaction system of Aa1+Aa2+…+Aai (an A group can react with an A group) and of the reaction system of Aa1+Aa2+…+Aa+Bb1+Bb2+…+Bbj，(an AA group can react with a B group)have been derived by using the theory of stochastic cascade process and by using Good’s results of multidimensional Lagrange expansion．These distribution func-tions are identical with those obtained from classical combinational theory which was established by Stockmayer．Ftom the results thus established，two distribution fune-tions may be applied to the range beyond the gel point．