The invention discloses a three-main truss bolt-welding combined cable-stayed bridge full-section structure and a total splicing truss width control method thereof. The three-main truss bolt-welding combined cable-stayed bridge full-section structure includes a middle truss piece arranged between two side truss pieces. Road bridge floor plates are arranged on the upper ends between the middle truss piece and the two side truss pieces. Railway bridge floor plates are arranged on the lower ends between the middle truss piece and the two side truss pieces. The road bridge floor plates are connected to the middle truss piece and the side truss pieces through welding seams and the railway bridge floor plates are connected to the middle truss piece and the side truss pieces through welding seams. Through the control of the manufacturing precision of the middle truss piece, the side truss pieces, the road bridge floor plates and the set welding shrinkage allowance, the reasonable selection ofwelding sequence in a process of three-dimensional total splicing of the full section and the use of truss width control limit devices in process of welding deformation, the three-main truss bolt-welding combined cable-stayed bridge full-section structure and the total splicing truss width control method thereof realizes the total splicing truss width control of the three-main truss bolt-weldingcombined cable-stayed bridge full section and ensures that the acceptance size of the total splicing of the full section meets the design requirements.