The　world　is　full　of　complexity.　Better　understanding　of　the　complex　system　can　help　us　to　make　better　decisions.　Thus,　the　way　to　show　and　understand　complexity　receives　a　lot　of　attention　from　researchers　and　teachers.　In　this　study,　we　try　to　find　out　that　phase　diagram　VS　stock　&　flow　diagram,　which　one　is　more　helpful　to　understand　a　simple　complex　system.　A　simple　model　with　only　one　stock　is　used　in　the　experiment.　Subjects　without　any　system　dynamics　background　are　provided　with　full　information　but　different　representations.　The　experiment　result　shows　that　the　ignorance　of　nonlinearity　and　feedback　persists　in　all　of　the　subjects.　No　matter　what　they　are　presented,　phase　diagram,　stock　&　flow　diagram,　or　both,　their　performances　are　statistically　the　same.