The invention discloses a building formwork system. According to the building formwork system, a cushion lining piece is arranged at one end of a formwork wall plate, the first end wall of a first cushion piece body of the cushion lining piece is mounted at the end of the formwork wall plate, and the second end wall of the first cushion piece body of the cushion lining piece abuts against a building body. The first end wall of a second cushion piece body of the cushion lining piece is used for being mounted at the external fixed end, and the second end wall of the second cushion piece body abuts against the second end face of the first cushion piece body, so that the exposed-out bottom position of the building body is well blocked, and the mounting compactness is improved.