The invention relates to a manufacturing method of a large
steel box girder. The manufacturing method comprises the following steps of: manufacturing a unit piece, assembling and pre-splicing girder sections, hoisting a
steel box girder on a construction site, and performing
welding, wherein the step of manufacturing the unit piece comprises: designing a drawing by using AUTOCAD
software, performing modeling, determining a theoretical size, and determining
welding and
processing compensation amounts; and the step of manufacturability analysis comprises: A,
welding manufacturability test, B, manufactured bridge actual measurement data and C, part
machining requirements. Compared with the prior art, the manufacturing method disclosed by the invention has the advantages that a forward mounting method and a reverse mounting method are adopted, namely, bottom plate unit pieces are firstly assembled, then web unit pieces, diaphragm plate unit pieces, panel unit pieces and
cantilever unit pieces are sequentially assembled, and the
cantilever unit pieces adopt the reverse mounting method. The method has the
advantage that most of weld joints are welded in a horizontal or climbing position. During welding,
welding deformation is effectively controlled by utilizing the principles of constraint, self-constraint, strong constraint and flexible constraint, so that various geometric dimension deviations of all steel box girders are within a very
small range.