Abstract: Ammonia pollution becomes one of most crucial factors in the decline of the surface water quality and the deterioration of the aquatic ecosystems in China. This paper studies the impact principles on the quality of river water and the sorption and retention characters from the riparian reed,on the basis of site comparison experiments.Theoretical analysis had been per formed and some conclusions had been obtained that the conflux of rainstorm at the beginning stage had the worst influence on the quality of river water,and the sorption abilities of ammonia by riparian reed zone were influenced by growing stage of the plants,the concentration of ammonia in rivers,the rate of water flow and some meteorological conditions. Furthermore differences of the attenuation coefficient and decrease amount of ammonia under the conditions of existing riparian reed zone and non-reed zone had been achieved through numerical simulation and parameters optimize method. The changing principles and impact factors of them had also been found,which would provide scientific foundations for aquatic ecosystem restoration and water quality prediction.