Kansai international airport was newly constructed and opened off Senshu city in the bay of Osaka. This airport was built on an artificial island newly reclaimed from the sea. Although other similar airport projects are also being discussed in Japan, application of reclamation system in the deeper sea is very difficult to realize because of the necessity of the massive sand for the filling of the land. Long period of construction and environmental impacts are also obvious defects of this system. On the contrary, an airport with floating system clearly has advantages in some points. Especially, it is considered to give less damage to the environment than reclaimed one. The authors wish to show numerical simulations by means of multi-level model to discuss the effects of artificial islands on ocean current. The boundary conditions of floating islands for numerical model are newly treated in this paper. By means of the multilevel model, differences of current pattern around floating and reclaimed islands are discussed in cases of simplified rectangular bay, Osaka Bay, and Tokyo Bay. It is clarified that a floating airport changes the current pattern less than reclaimed one.