The dragon door crane is mainly used for outdoor cargo yard, material and bulk loading and unloading. Its metal structure like the door frame, bearing the main girder, the installation of two supporting feet, can be directly on the ground of walking on the orbit, both ends can be overhanging cantilever girders. The gantry crane has the characteristics of high utilization, wide range of operation, wide adaptability and strong universality, and is widely used in port yard.