Taking Xinggu section which is from Xingshijie to southern segment of ancient channel in the middle route of south-to-north water transfer project (Xing-Gu segment) for example, the paper established the model of water quality simulation in the section and simulated the rule of pollutant dispersion. According to the simulation results, it established emergency decision system in accordance with the amount, location and alarm response time of pollutant to carry out fast interpolation and output peak concentration, location and range of pollution zone, and compared which with the simulation results. The result shows that the fast emergency decision system can meet the accuracy requirement of decisiion,the peak concentration of pollutants and simulation results differ in the range of 0.10 mg/L, the difference of location of pollution cloud cluster getting to is within 500 m, the length difference of pollution cloud cluster is in the range of 100m.The system has the features of fast response, accurate prediction.The Xinggu section is a tributary of multi-channel.Compared with the method of numerical simulation ,the interpolation method can save time of quick decision.