The invention discloses a river basin runoff forecast correction method and system. The method comprises the steps of obtaining real-time river basin runoff forecast data, corresponding rainfall data and runoff measured data, extracting historical data, calculating a correlation coefficient vector Vr of each set of historic runoff process data and other sets of historic runoff process data, dividing the historic runoff process data into two categories according to vectors, building a nonlinear forecast model for each category of the runoff process data, performing correlation analysis on the real-time river basin runoff forecast data, the corresponding rainfall data and the historic runoff process data, selecting the forecast model with the maximum coefficient as a correction model, adopting the real-time river basin runoff forecast data and the corresponding rainfall data as the input of the selected correction model, and outputting the corrected river basin runoff forecast data calculated by the selected correction model. According to the river basin runoff forecast correction method and system, the runoff forecast correction precision is improved, and the important decision information guidance is provided for reservoir optimal dispatching.