A serial Grey Modle GM (1.1) for predicting sedimentation in Chaochu lake was established,and also,the principles of seletion of the length periods of GM (1.1) were suggested in this paper.IN considering the increasing tendency of soil erosion in the watershed for years,the model must be made to have a high accuracy than that of the nonlinear regression modeling in sedimentation prediction.Meanwhile,the variables to be predicted can not depend on any other stochastic ones,being more stuible for serial prediction than the non-linear regression modeling.Finally,this paper suggests some ways of controlling sedimentation in Chaohu lake.