The Cantilever Precast Segments Launcher is a special launching equipment for building mainspan of cable-stayed bridge. The working mode ofthis launcher is that lifting precast segments from boat which under the bridge , and the launcher at the cantilever state. The launcher will autoforward after precast segments assembling finish in the air, so one cycle completed. The characteristic of this launcher working have three points:one, high head of lifting;two, heavy load at cantilever state; three, the assmbly process of heavy precast segments girder precise contraposition.