Initial hull form of 10 G/T and 40 knots class coastal patrol boat is newly developed. The resistance performances are experimentally and numerically investigated by model test and CFD technique. The effect of initial trim and a fin attached at hull side are studied together. Wave patterns are observed to make clear the relation between the performance and the wave characteristics. It can be found that the initial trim plays a role in increasing the resistance performance above a certain velocity, and the CFD technique can be used at the initial design stage of a high-speed planning boats.