A stochastic typhoon model, simulating typhoon parameters during a certain long period with the Monte Carlo method, have been developed based on the statistics of past typhoons around Japan. This study assumed a simple variation of typhoon parameter fields due to global warming and improved the stochastic typhoon model to give stochastic typhoon parameters in future climate. Then the study computed the storm surges by the stochastic typhoons in Seto Inland Sea and estimated the extreme-value function of the tidal levels. The result shows that a higher tidal level than the present design one for storm surge defense facilities may appear with a long return period even in present climate. Both typhoon intensity increase and mean sea level rise may increase the frequency of a disastrous high tidal level. The regionality related to the bathymetry can be found in extreme tidal levels.