A biomimetic manta ray underwater glider actuated by buoyance is presented. Firstly, the hydrodynamic structure shape of the biomimetic manta ray underwater glider is established with reference to the appearance of manta rays. Secondly, the steady motion of the biomimetic manta ray underwater glider in the vertical plane is analyzed and a simple kinematic model of the biomimetic manta ray underwater glider is built. Thirdly, the hydrodynamic performance of the biomimetic manta ray underwater glider is analyzed through commercial software CFX, and the variation of lift and drag alone with the changing of the net buoyancy and center of gravity position is estimated. Finally, compared with classical shape designs in lift-drag ratio and gliding speed, the biomimetic manta ray underwater glider have better hydraulic performances with large angle of attack and small attitude angle.