In the present paper, guess calculations of the residual deformation and stresses in a ship's hull caused by welding are treated. The problem of this kind becoms very important since the welding technic was adopted in the ship-building, industry and some investigations in this field are presented recently by some investtigators. But the phenomena seems to so complicated that the exact calculation of this problem is almost incapable, and the author treated it, simplifying the problem, by the simple beam theory in order to know the order of the stress, The result gained shows the stresses under ordinal residual deflection are in elastic region, but the assumption assumed is too simple and so the author intends to treat it more exactly.