The Monte Carlo arithmetic invented by Gillespie was used to model the random degradation reaction of linear polymers．The number of molecules having different degree of polymerization was given at anytime in the degradation process．It was found that the number of molecules of high degree of polymerization (DP) decreased rapidly at the very begining of the degradation process．At the same time

the number increase of low DP molecules increased with decreasing the DP of molecules

and a smooth DP distribution was obtained．