Generally, underwater gliders do not have separate propellers to move forward. They are driven from propulsive force by difference between their buoyancy and gravity. Also the attitude of a underwater glider is controlled by changing the relative position of the buoyancy center and mass center. The proposedunderwater glider in this paper is designed to use an inner buoyancy engine of cylinder-piston type and movable mass controller, with which buoyancy and attitude can be controlled. The buoyancy engine changes the volume of a ballast tank to make a heave motion of the underwater glider. The movable mass, which enables translational and rotational motion, makes a pitch and roll motion of the underwater glider. In this paper, as a basic research of the underwater glider, we derive nonlinear 6DOF dynamic equations that only consider the kinematic characteristics, such as the location of the movable mass, and the piston of the buoyancy engine. Using these equations, we performed dynamic simulations of the proposed underwater glider, and verified the suitability of the design and a dynamic performance of the proposed underwater glider.