This paper proposes a new method on attitude control of an underwater vehicle by using five ABTs (Attitude Ballast Tank). A pipe is connected to the bottom of the ABTs and transfers water by a pump, while another pipe is connected to the top of the ABT transfer air. The buoyancy center of the underwater vehicle can be changed by means of the water transfer. The changes of the center of gravity and the buoyancy central are estimated by a Lagrangian function which is similar to that for an inverted pendulum. The controller in this paper is designed by modeling of the underwater robot and selecting suitable gains of PD controller which has fast response characteristics. This paper shows the possibility of the attitude control of an underwater vehicle by changing the center gravity and the buoyancy center of the vehicle using very low power consumption.