Since the1940s, Stockmayers has proposed that weight average functionality should be used, because the probability to encounter the junction of different functional groups depends on the mole fraction of reactive groups. Most of these theories were based on the assumption that the weightaverage molecule weight or DPw diverges to infinity when gelation occurs. They thought that when DPw and Mw diverges to infinity，DPn and Mn do not diverge to infinity at the same time. While, Mw and Mn are not an absolute exponential relationship theoretically. When DPw and Mw diverge to infinity, DPn, Mn and fn diverge to infinity at the meantime, which can be concluded as the following basic equation: