We conducted a nitrogen removal test using floating islands in polluted rivers. The results show the nitrogen removal efficiency of Cyperus alternifolius exceeds that of Vetiveria zizanioides which in turn is greater than flagleaf. The relationship among removal loading, coverage rate and inflow loading was studied. The boundary of coverage rate was 30%. There was a significant change in the relationship between removal loading and coverage rate. The relationship between removal loading and inflow loading follows a quadratic function. The appropriate coverage rate and inflow loading were found based on this test.