The invention provides a shear force connecting part, a combination beam comprising the shear force connecting part and a construction method of the combination beam, and relates to the technical field of support beam structures in a road bridge and a building. Aiming at the problems that according to an existing method, additional stress is exerted on a shear force connecting part, so that pre-pressing stress of a concrete slab is poor in effect, and according to a combination beam, stress weak links or corrosion channels exist on connecting interfaces of different materials, the connecting part comprises a pre-buried steel plate, and at least one set of high-strength bolt connection pairs is arranged on the pre-buried steel plate. Each high-strength bold connection pair at least comprises a bolt, a number-one fastening nut and a number-two fastening nut, wherein the number-one fastening nut is connected to the fixed end of the bolt, and the number-two fastening nut is connected to the free end of the bolt. The construction method includes the steps that step1, the free ends of the bolts in the shear connecting parts are buried in a poured concrete slab, and the number-one fastening bolts are loosened; step2, after the concrete slab reaches designed strength and an age, pre-stress tensioning is performed on the concrete slab; step3, the number-one fastening nuts are tightened, and construction of the combination beam is finished. The construction method is particularly suitable for constructing the support beams in the road bridge and the building.