Grey-Markov forecasting floods is presented and the corresponding model is applied and tested with the Chaohu Lake Basin as the study area.The result shows that combination of the grey system GM (1,1) forecasting model with Markov Chain is a new way for understanding water rule.Grey System GM (1,1) Forecasting Model and Markov Chain is combined based on statistic analysis,with which the other influence factors will not be considered.Therefore,the forecasting results will be more accurate.