Through application of grey forecast theory,the paper built GM(1,1) forecast model of pollution water quality change trend of the Longjiang River burst and modified the model residual. The results show that the GM(1,1) model after residual modification is more reasonable , and prediction accuracy is obviously improved.The residual GM(1,1) model can effectively forecast the trend of water quality during a short period in sudden water pollution accidents,provide reference for the relevant department to adopt the corresponding emergency measures and reduce the risk of accidents.