The invention discloses a combined formwork system for round tunnel concrete pouring. The combined formwork system is composed of a top fixed formwork, two side fixed formworks and a sliding formworks; the top fixed formwork can telescopically support and cover the 120-degree arc surface of the top arch through a top formwork support, the two side fixed formworks can telescopically support and cover the 60-degree arc surfaces of the two side walls through two side formwork supports on the two sides, and the sliding formworks are parallelly arranged in two rows along the tunnel; the surfaces ofthe frameworks are provided with arc surfaces matched with the round tunnel concrete pouring surface, and through supporting of multiple sliding formwork hydraulic jacks, each row of sliding formworks are driven to move on the two sides of the 120-degree arc surface of the bottom arch through a sliding formwork traction moving system. The poured combined framework can be subjected to full-face primary pouring and forming, the construction efficiency is high, the quality defects that air bubbles, water bubbles and holes exist to the surface of concrete are overcome, and the construction seam defect can be overcome through the sliding formwork structure by adopting the manual plastering technology.