Abstract: The purifying effect of reed on lake phosphorus content with different water depths in the Dongting Lake was studied. The results showed that reed played an important role in reducing lake phosphorus content. During the growth season, the highest total phosphorus (TP) removal rate of shallow and deep water area of reed root zone were 55% and 25%, and the surface removal rate of 35% and 20%, respectively. And in the withering state, the TP removal of root zone could be up to more than 30% and 20%, and maintained 15% in the surface layer. The result shows that TP can be effectively reduced through timely harvesting of reeds in the lake.