The invention discloses a river water quality prediction and an evaluation method of water quality influencing factors. The method comprises the following steps: firstly, extracting historical data of river water quality and watershed characteristics of corresponding sampling points to form an original training set; Secondly, through the bagging algorithm, randomly selecting samples from the original training set, and constructing several sub-training sets . third, generating a decision tree by selecting split attribute according to that characteristics of different watersheds, and constructa random forest model according to the decision tree; Fourth, evaluating the simulation effect of the model; 5, acquiring watershed characteristic data of a point to be predicted, putting that data into a stochastic forest model, and obtaining corresponding water quality prediction data; Sixth, assessing the impact of different basin characteristics on river water quality. The relationship modelbetween watershed characteristics including watershed hydrology, climate, geographical characteristics, seasonal factors, human influence and the like and river water quality is built, river water quality index data is accurately predicted according to watershed characteristics of a target point and importance of the influence of a watershed characteristic on water quality is evaluated.