The author introduces the velocity potential of the displacement ship by making use of Green's function or the fundamental singularity. This method is more rational than the one we have had. and deduces the result that singularities which are on the water line of the ship surface are of negligible order especially when the surface of the ship near this water line is vertical. Nextly, he obtains the integral eqations of solving the problems by the aid of Green's function in the potential theory in cases of submerged bodies and floating ships. Two applications of these eqations are developed in the paragraph 4 and 5. The one is of the problem of deeply submerged and high speed body. This is not very interesting, , but gives a mathematical foresight to the solution. The other is of the wave resistance of ships at very low speed. In the case of a hemisphere, the solution of the integral eqation tells us the wave making character at very low speed is confined itself in the neighbourhood of the bow. Thus obtained resistance formula is very simple and seems to be applied to the ordinary ship at very low speed so that may be useful.