In this paper applying the thin wing theory, the effect of immersion on the characteristics of the submerged hydrofoil is examined. The main problems considered are as follows; (1) Substituting the submerged hydrofoil by a single vortex, the fundamental properties of the effect of immersion are clarified. (2) Expressions for the lift, wave resistance and profil form of an arbitrary vortex distribution are introduced. (3) An applicability of thin wing theory to the submerged hydrofoil is discussed. (4) A relation of types of vortex distribution to the wave resistance is examined.