It has been proved by systematic analysis and research that the sagging and hogging bending deformation of the navigating ship will exert a certain effect on the clearance of the movable end support of the ship longitudinal shaffings, which should not be negligibie especially for the longitudinal shaftings installed on the upper deck or the bottom. The author of this article has proposed a new calculation formula for designing optimally the clearance of the movable end support of the longitudinal shaftings. Because the formula includes more objectively the effect of the sagging and hogging bending deformation of the navigating ship on the clearance of the movable end support of longitudinal shattings, the caiculating according to the formula will make the clearance design of the movable end support of the ship longitudinal shallings hecome safer and more suitable to actual conditions.