Surrounding fluid of a struck ship contributes to make upright position after ship collision, also which can affect the amount of flooding. The unique way to consider the fluid is known as fluid-structure interaction technique, but requires quite high costs. This paper provides a very efficient way to consider fluid effect surrounding striking and struck ships in case of collision. The new technique can consider hydrostatic and hydrodynamic loads without modeling the fluid. The hydrostatic and hydro-dynamic forces were realized without fluid modeling by applying a newly developed user-subroutine of a commercial FE code. The developed technique was verified through various simple load case simulations for a box model. A collision analysis of the model composed of a ship-shaped box girder and wedge type indenter was carried considering the buoyancy and drag forces using the developed user-subroutine. There were very critical differences between before and after consideration of the fluid.