Molecular dynamics simulations were performed to investigate the influence of molecular weight on the interpenetration process of two initially isolated globule-chains. From molecular weight lower and higher than the critical molecular weight, the analysis of the simulation result indicate the duration of interpenetration has the relationship with chain length: tau similar to N-2, which is different from that of the relaxation time in reptation model. It also shows that the interaction between chains measured by the mean force increases with the increment of chain length, and a turning point was found at the position corresponding to the critical molecular weight. Before the turning point, the mean force increases fast versus molecular weight, and after that the increase turns to be slow. Through correlating the simulation result with the experimental tensile strength of polymer films, it shows that the interpenetration of the chain segments with critical molecular weight is necessary for the formation of entanglement structure.