In order to quantify the water quality pollution situation of the monitoring sections and explore the variation of water quality risk, the water quality risk of the waterway of Poyang Lake to Yangtze River was evaluated based on the monthly water quality deterioration rate of different monitoring sections. The water quality monitoring data of Wucheng, Duchang, Laoyemiao, Xingzi and Hamashi sections were selected to simulate the risks of exceeding water quality standards under different scenarios, and the spatial and temporal variation of water quality risk in the waterway was discussed. The results show that the monthly deterioration rate of water quality in Poyang Lake fits the p-Ⅲ distribution. Because the water quality risk of the section is defined from the perspective of the probability of occurrence of harmful events, the water quality problems faced by the waterway of Poyang Lake to Yangtze River can be accurately described, and the proposed risk threshold can reasonably characterize the risk level. The main indices affecting water quality of the waterway are TP , pH and COD. TP is the control index that causes the water quality of Hamashi to exceed the standard, and the probability of exceeding the standard is 12.29%; the control index of Wucheng and Laoyemiao is COD, with the probability of exceeding the standard of 2.58% and 2.73% respectively; and pH is mainly responsible for the deterioration of water quality in Duchang and Xingzi, and the probability of exceeding the standard is 1.82% and 3.29% respectively. According to this method, the probability of exceeding the standard of relevant water quality indices can be predicted, the water quality risk level of the section can be determined, and the main indices that may lead to harmful water quality events can be found out, which can provide technical support for the accurate management of water quality of the target water body.