Not describing the complex mechanism of backwater effect among Jialingjiang River,QujiangRiver and Fujiang River directly,but setting up a time-variant linear model, the paper presents a on-linereal-time hydrological forecasting method.The self-adapting filter algorithm revised by the author is used for theon-line recognition of parameters.The integral input and multiple inputs are studied respectively.The model isapplied to Jialingjiang River Basin for on-line real-time flood forecasting.The results of 65 flood proeesses showthat the model and algorithm are simple and feasible,the parameters and initial values are stable,and the agree-ment between measurements and predictions is good.