Effect o￡ the carbon sources of three plant straws-reed, branch and reed + branch supplement in constructed wetland. The straws filling surface layer (0-5cm) and middle layer (30-35cm) on nitrogen removal was studied. Experimental result shows that, supplement constructed wetland with plant straw under the condition of experimental influent could enhance system TN removal rate from 44% to 53%-66%, and the type difference of plant straws has no significant effect nitrogen removal. Supplement of these three plant straws in middle layer can reach better nitrogen removal efficiency and have stronger ability to resist the impact of influent nitrogen loading. Nitrogen form variation with distance indicates that, supplement of plant straw can clear nitrate nitrogen and nitrite nitrogen accumulation induced by lack of organic caibon, thus improves nitrogen removal efficiency. The plant straw supplement in middle layer, because of not interfering with the process oi nitrification of influent ammonia nitrogen can produce more denitrificalion substrates-nitrate nitrogen and nitrite nitrogen, having better nitrogen removal efficiency than supplement in surface layer.