With the development of autonomous underwater vehicle (AUV), the long distance and large depth is the main development direction of AUV. Using the equipment of buoyancy adjusting instead of the motors of the bow and stern channel can save energy and increase endurance of AUV. Based on the oil capsules device of buoyancy adjusting in this paper, designed two different schemes: one is that oil capsules are installed outside of the AUV; the other is that oil capsules are installed inside of the AUV. We calculate the resistance of two schemes based on CFD. By comparing the resistance under the same scheme at different speeds (3km, 4km, 5km) and in different schemes at the same speed, we can get the most optimal scheme.