Abstract:  Based on a drilling vessel， a model test was carried out in the multifunctional towing tank of Shanghai Jiao Tong University， combined with CFD numerical simulation， in order to study the added resistance of recessing type moonpools. It is found that additional resistance of moonpool is significant and may exceed 50% at high speed. Comparing the resistance of different recessing moonpools of this drillship under the draft of 8.53m， it shows that moonpool with postposition recess has better drag performance than that with preposition recess. Besides， inclined fore wall and rear wall of moonpool can bring a certain amount of drag reduction. Water oscillation caused by periodic eddy during the navigation of drillship is the main cause of added drag. After having optimized the shape of the moonpool， the water oscillation inside the moonpool is more gentle， which reduces the drag increase of the moonpool. These conclusions can provide reference for the drag reduction design of moonpool.