The rapid development of China’s economy has led to a sharp increase in the municipal solid waste (MSW). China has promulgated the MSW mandatory classification policy. The implementation effect of such mandatory policy is an important concern to the government, scholars and the public, but has not been extensively studied. This paper explores the implementation effect of such policy through assessing the waste classification behavior of residents based on the Cellular Automata model. The simulation results show that the residents will not adjust their MSW classification behavior during the time period when the mandatory classification policy is not implemented.But when the mandatory classification policy is imposed, the residents will adjust their classification behavior over time from t=100 to t=300.The results indicate that the extent of residents’ participation in waste classification varies by different enforcement intensity .The higher the intensity is, the more rapidly residents’ MSW classification behavior improves.The results also indicate that the extent of residents’ participation in waste classification varies by different urban population size. The larger the urban population size is, the higher the proportion of classification participation is.