In greenhouse,three different simulated constructed wetland systems were built up with slag,zeolite and paddy soil,respectively,as substrate,and with Oenanthe javanica,Lolium mutliflorum and Vetiveria zizanioides,respectively,as vegetation. Efficiencies of the three wetland systems removing nitrogen and phosphorus from domestic sewage were studied as compared with that of the floating-bed plant system(no substrate). Results showed that when nitrogen and phosphorus load was low and the hydraulic retention time was 6 days,the constructed wetlands of slag,zeolite and paddy soil displayed high efficiency in removing total nitrogen(TN),ammonia nitrogen(NH₄⁺-N)and total phosphorus(TP),with an average removal rate of over 91.0% for all the three,but low efficiency in removing nitrate nitrogen(NO₃^--N)with a rate ranging from 58.0% to 85.5%. When nitrogen and phosphorus load was high,the floating-bed plant system was much lower than the three simulated ones in removing efficiency. In terms of removal amount,the paddy soil system was lower than the slag and zeolite ones. In the floatingbed plant systems,negative increase in NO₃^--N removal amounts led to decrease in TN removal amounts,but its NH₄⁺-N removal amounts was significantly higher than those in the three simulated wetland systems. The removal amounts of TP in the Oenan the javanica and Vetiveria zizanioides floating-bed systems were also higher than those in all the three simulated wetland systems. Different plants were different in ability to assimilate nitrogen and phosphorus. The four wastewater purifying systems with Lolium mutliflorum as vegetation regardless of substrate,assimilation of TN and TP by the plant was the main mechanism for TN and TP removal. TN and TP uptake by Oenanthe javanica and Vetiveria zizanioides were much smaller than those by Lolium mutliflorum in the three simulated wetland systems,suggesting that Oenanthe javanica and Vetiveria zizanioides assimilation of TN and TP contributed partly to TN and TP removal in the three systems. However,the assimilation of P by Oenanthe javanica and Vetiveria zizanioides was the main mechanism for TP removal in the floating-bed plant systems.