Sea level rise,which is a focus topic of global change study,will cause extreme high water level events bringing a series threat to the coastal city of economic development and social life. Therefore,in the background of the current climate change,we carry out risk assessment of extreme high water level events is particularly important and urgent. We introduce frequency risk ideology to construct frequency risk model and evolution index system containing frequency. Intensity and consequences of the extreme high water events. We established this model based on Gumbel extremum method,grey Verhulst model and ArcGIS platform,taking Ningbo city as an example to study the risk of the economic losses which Chinas coastal city has suffered under different extreme high water level scenarios with the climate change. The results show that the occurrence frequency of extreme high water level events will be far greater than the current bank coastal city based on many domestic and foreign scholarspredicting; the prevention ability will be greatly reduced. we also give the quantitative assessment of different extreme high water level eventspotential threats to Ningbo and its economic losses.