Combined with the construction of 800 t dock gantry crane, in order to solve the practical problems during the construction, the girder camber design method is given. In order to ensure the girder construction quality, the construction technology of girder section is established, and the treatment methods are proposed for some specific problems to ensure the girder construction precision. After the gantry crane is completed, the camber measurements under different working conditions are taken to check the construction precision. The measured values are close to the designed values, which indicates that the construction technology adopted is reliable and can provide reference for the construction of similar large gantry crane.