The indoor hydrolysis simulation experiment was carried out with the aboveground stems and leaves of five dominant plants in the drawdown zone of Sanhekou reservoir, namely, Artemisia carvifolia Buch-Ham, Artemisia argyi Levl. et Van, Eclipta prostrata L., Bechmannia syzigachne(Steud.) Fem and Polygonum lapathifolium L. as the samples and the reservoir water as the experimental raw water. By measuring the basic water quality indices and the nutrient concentration of nitrogen and phosphorus of the overlying water, we investigated the impact of the plants in the drawdown zone on the water environment and the release characteristics and load of different forms of nitrogen and phosphorus nutrients after hydrolysis. The results showed that when these five plants were inundated, the color of the overlying water deepened, peculiar smell occurred, pH value decreased, turbidity increased, electrolytic rate increased and dissolved oxygen decreased; nitrogen and phosphorus nutrients were released, and the average release amounts of total nitrogen and total phosphorus were 4.06 mg/g and 0.78 mg/g, respectively, among which, the particulate nitrogen and phosphorus accounted for 43.2% and 36.2% of total nitrogen and total phosphorus, respectively; at the initial stage of reservoir impoundment(30 d), the nitrogen and phosphorus load released by vegetation in the drawdown zone to the water body can reach 40.4 kg/hm2 and 7.6 kg/hm2, which in turn will affect the water environment safety of the Sanhekou Reservoir.