In view of the additional resistance of moonpool in drilling vessel, the influence of the moonpool shape on the additional resistance of the drilling vessel is studied. Based on the study of unsteady flow characteristics in moonpools in different shapes and the comparative analysis of the additional resistance of drilling vessel, the influence of the moonpool shape on the additional resistance is discussed. The CFD analysis shows that the additional resistance is increased by the fluid blockage effect and vortex motion in the moonpool of the sailing drilling vessel. By optimizing the shape and structure of the moonpool, the wave height and vortex intensity in the moonpool can be reduced effectively and the navigation performance can be improved.