The utility model discloses a three-main-truss bolting and welding combined cable-stayed bridge whole section structure. The truss comprises a middle truss piece arranged between two side truss pieces, highway bridge deck plates are arranged at the upper ends between the middle truss piece and the two side truss pieces, railway bridge deck plates are arranged at the lower ends between the middle truss piece and the two side truss pieces, and the highway bridge deck plates are connected with the middle truss piece and the side truss pieces through welding seams, and the railway bridge deck plates are connected with the middle truss piece and the side truss pieces through welding seams. According to the structure, the manufacturing precision of the middle truss piece, the side truss pieces,the highway bridge deck plate and the railway bridge deck plate is controlled, and the welding shrinkage allowance is set; the welding sequence is reasonably selected in the whole-section three-dimensional total splicing process, the truss width control limiting device is used in the welding deformation process, three-main-truss bolting and welding are combined with cable-stayed bridge whole-section total splicing truss width control, and it is guaranteed that the whole-section total splicing acceptance check size meets the design requirement.