After the theoretical analysis of the greysystem model (GM) method in this paper, it is be-lieved that the feature of rainfall reflected by the GM model is similar to the accumulated efficiency of long- termwater and sediment variation. 4 GM models are used to predict the variation tendency of the flood periodicaland annual water and sediment series respectively. The results show that GM(2,1)is better than GM(1,1) and GM(1,2) in predicting water and sediment variation.