A coring device has core drilling tool, a core catcher, a rock core barrel, a drilling machine outer cylinder, a flap valve and an inner rod for pulling the rock core barrel. The core catcher is provided inside the lower end of the rock core barrel. The core drilling tool includes an outer core tube and a hollow drill bit. The upper end of the outer core tube is connected to the lower end of the drilling machine outer cylinder. The lower end of the outer core tube is connected to the drill bit. The lower end of the inner rod protrudes into the rock core barrel and is movable axially by a certain distance relative to the rock core barrel. The flap valve includes a valve seat and a sealing flap. The valve seat is coaxially mounted on the inner wall of the drilling machine outer cylinder.