The invention relates to a day-ahead hydrological forecasting error correction method and system. The method comprises the following steps: calculating a hydrological forecasting process forecasting value and a forecasting error matrix percentage interval; carrying out K-means clustering on the forecast value and the forecast error matrix percentage interval; establishing a typical category regression model of a forecast value and a forecast error matrix percentage interval after K-means clustering; and establishing a forecast value correction model of typical category regression model forecast error estimation. A day-ahead error feature identification method considering error time sequence modal decomposition and error feature classification is adopted to decompose, identify and positionan error dynamic process, and then feature matching is carried out in practical application, so that the day-ahead hydrological forecasting level is improved.