The slow underwater speed of the underwater glider necessitates a long time to reach the predetermined operation area. Therefore, this paper proposes the design of a rectangular breakable wing with subsonic symmetrical airfoil to enable air gliding functionality for the underwater glider. A numerical model of the Trans-medium glider is established to study its longitudinal plane dynamics under the influence of the wing. The results demonstrate that the Trans-medium glider exhibits a large minimum flight speed and favorable lift-drag ratio and pitch characteristics in both air and underwater gliding.