Taking the climate scenarios RCP2.6 released by IPCC AR5 as background,the highest water level of ZHAPU in the coming decades was predicted by using model of grey-mean generating function based on the highest water level data of ZHAPU in Zhejiang province during 1995 to 2012, and the recurrence intervals of the extreme high water level of ZHAPU during different predictive periods were calculated by Gumbel curve method according to different sea level rise situations. Results show that the model of grey-mean generating function has higher accuracy and variability in simulation and prediction of extreme high water level, but there is a slight lack of forecasting extreme value, and it is more suitable for average state forecast. The recurrence period of extreme high water level is going to change dramatically with climate change, and after two or three decades, the return period of extreme high water level maybe change from a hundred year to twenty or thirty years or so.