Abstract: Based on the statistical/kinetic method previously presented by the authors,a partition model of primary chains between sol and gel is developed.A model of average molecular weight of the sol is also proposed.From computer simulation,it is found that the chain length in the gel is much bigger than that in the sol and once passing gel point,the molecular weight decreases sharply,depending on reactivity ratio.The present model is successfully applied to predict the development of molecular the weight of sol in the vinyl chloride/diallyl phthalate suspension crosslinking copolymerization.