By investigating the distrihutons of microorganisms and growth of macrophytes.the role of medium·macrophyte and microorganism in wastewater by artificial wetland has been studied and the mechanisms of N,P and COD elimination have been discussed. From studies on the artificial wetland with cattail(Typha angustifolia)and rush (Juncus effusus)·it had a trend that reproductions of microorganisms in spring and summer were 1arger than those in autumn and winter. The remoral rates of KN.NH4+-N were significantly related to the number of bacteria,protozoa and algae in control(P < 0.05). Tbe contam inates remora capacities of artificia wedands were also related to the growths of macrophytes. Parts of nitrogen, phosphorous were fixed by exchanging, complexing. precipitating and adsorbing in media. The results indicate that the collaboration of medium,macrophyte and m icroorganism is the mechanism of putlying wastewater in artificial wetland. Medium with granite and viSCOUS soil is better for removing phosphorous.