Abstract: Based on the different hydrological and hydraulical conditions of channel reservoirs during a hydrological year, the prediction model of their total phosphorus (TP) was established by combining the 2- D straight river model and the polar coordinate diffusion model proposed by A B Karaueshev (A B Kapayщв). Then the TP prediction model was applied to simulating and forecasting the variation of TP concentration in narrow channel reservoirs with a water depth of less than 5 m. By taking the Sanjiang reservoir in Mianyang as an example, the relative error between predicted and observed results of its TP concentration is less than 10%.