The invention relates to a corrugated steel webplate combined box girder floor system for a cable-stayed bridge and a construction method thereof, and belongs to the technical field of bridge structures. The corrugated steel webplate combined box girder floor system comprises a precast concrete plank and a cast-in-place concrete seam, wherein the precast concrete plank is positioned on a steel box girder and is integrated with the steel box girder into a whole; the steel box girder is formed by welding a top flange steel plate, a corrugated steel webplate and a steel plate at the bottom of the box girder; a box girder baseplate stiffening rib and a diaphragm plate are welded in the steel box girder; the diaphragm plate comprises a top flange steel plate of the diaphragm plate and a steel webplate of the diaphragm plate; a toggle pin connecting piece is welded on the top flange steel plate and the top flange steel plate of the diaphragm plate; and a steel anchor pulling plate and a steel sleeve are welded on the top flange steel plate. The corrugated steel webplate combined box girder floor system simplifies the manufacturing process for the precast concrete plank, gives full play to the superior mechanical property of the corrugated steel webplate and the release action of the corrugated steel webplate on the creep effect of concrete shrinkage, improves the bearing capacity, stiffness and crack resistance of the structure, and improves the durability of the structure.