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　intensities.　The　higher　the　intensity　is,　the　more　rapidly　the　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.　Implications:The　implementation　effect　of　the　municipal　solid　waste　mandatory　classification　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　municipal　solid　waste　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.　The　results　also　indicate　that　the　extent　of　residents＇　participation　in　waste　classification　varies　by　different　enforcement　intensities　and　different　urban　population　sizes.