In shallow lakes, phosphorus will release from sediments to the overlying water when sediments are disturbed. Submerged plants can reduce the releasing. The impact of Vallisneria natans L. on the release of phosphorus from sediment to water were analyzed in a 40 day lab experiment with the independent hydrodynamic ecological flume under static and hydrodynamic conditions. This study was designed to provide scientific bases for estimating the impact of submerged plants on the release of phosphorus from sediment and the water environmental auality assessment. Results indicated that the phosphorus contents in sediment decreased by 21.8% under hydrodynamic condition, but decreased by 17.7% with the protection of V.natans L.. The phosphorus absorbed by V.natans L. in 1-4cm layer sediment was more than that in 4-8cm layer sediment. The dissolved phosphorus and the particulate phosphorus dramatically increased in overlying water under hydrodynamic condition and nitrate took a large proportion of total phosphorus in surface water, especially the particulate phosphorus. V.natans L. reduced the releasing of phosphorus from the sediment to the overlying water and large amounts of orthophosphate in the overlying water were absorbed by V.natans L..