In the past, a great many articles proposed theories and simulations of gel point which were basically suitable for the systems described by their ideal models, and there is no need to rederive the theoretical equations each time consequently. However, among all these literatures and models above, very limited articles have paid attention to the calculation of number-average functionality of the polymer mixture by stepwise polymerization reactions. While, it is a beneficiary to predict the average functionality theoretically as well as in practical applications, both for polymer structure design or scale-up industrial production.