CFD is recognized as a possible advanced tool to understand the performance of the underwater vehicle such as a hull resistance, a thrust force, motion in waves and so on. Focusing on the hull resistance, we conducted the investigation of the water resistance of the AUV PICASSO utilizing CFD and also conducting experiments to confirm the CFD simulations. After that, designing the hull form within the limitation of equipment arrangement to improve the hull resistance was conducted utilizing the CFD. And the experiment was conducted to confirm.