A combination of molecular theories and chemical reaction kinetics was employed to study the molecular structure evolution in the ethylene vinyl acetate and dicumyl peroxide, EVA/DCP, and metallocene polyolefin elastomer, m-POE/DCP crosslinking systems. Premixed EVA/DCP and m-POE/DCP compounds were cured at different temperatures and their gel contents were then measured. The values of crosslinking efficiency were evaluated and were then applied in the theoretical prediction of molecular evolution in a crosslinking process. The molecular weight distributions, gel time, relationships among gel content, degree of conversion, crosslinking density and processing time can all be predicted effectively. Information involving molecular structure evolution provides insights to practical process synthesis and material design.