The single main beam gantry crane mainly consists of a gantry, a lifting trolley, a crane operating mechanism, a driver's cab, and an electrical control system. The gantry is a box shaped single main beam with two legs. When the lifting capacity is below 20t, the trolley adopts a vertical anti roll wheel type. When the lifting capacity is greater than 20t, the trolley adopts a horizontal anti roll wheel type and runs on one side of the main beam. The main beam adopts a single beam offset rail form, with supporting legs and lower crossbeams forming an L-shape. Both sides of the supporting legs are generally equipped with cantilevers, which have strong over span capacity when lifting objects, making it easy to transfer objects from the inside of the span to below the cantilever.