Response of the East Asian Marginal Seas to an idealized typhoon have been investigated using a three dimensional ocean circulation model based on the HYbrid Coordinate Ocean Model (HYCOM). The model domain covers 115°E ~ 150°E and 15°N ~ 52°N with a quarter degree resolution aiming at those typhoons coming toward the Korean Peninsula. The maximum number of vertical layers is 30 but half of them can be used for the terrain following coordinate in the continental shelf region. Ocean response to the various typhoon parameters such as maximum wind speed or minimum surface atmospheric pressure, the sizes, and the translation speed with various tracks have been investigated. The well known surface cooling and/or upper ocean mixing has been simulated realistically and it's strength is highly related with the interaction time due to the typhoon translation speed as well as the mixed layer depth or the vertical structure. It is planned to including mutual interaction between the ocean and typhoon for the given track by coupling with a simple typhoon model for the development of the typhoon intensity prediction system.