Abstract: To investigate the purification capacity of Lythrum salicaria in aquaculture water, nine cement ponds in the same size used for culturing Cyprinuscarpio were randomly divided into control group(no plant), Lythrum salicaria group (with Lythrum salicaria ecological floating bed) and Eichhornia crassipes group(planting Eichhornia crassipes withthe same amount of biomass) and reared under the same prescribed conditions for60 days, respectively. Every13 days sample water was taken from each pond to test the content of the total nitrogen, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, total phosphorus, chemical oxygen demand(CODCr) and chlorophylla and a comparative study is done between the three. The results indicated that during the experiment significant difference is found in terms of the nitrate content and nitrogen content in Lythrumsalicaria compared with the other two groups(P<0. 05); No significant difference is found in terms of the other indices between the control group and the two experimental groups(P>0. 05); as for the value of the nitrate content and the CODCr content, the Lythrumsalicaria group