The invention discloses a sizing inner pipe for supporting a paper pipe. The sizing inner pipe comprises pipe wall arc plates, wherein the two sides of the arc surface of each pipe wall arc plate are respectively provided with an outer lip edge and an inner lip edge; the outer lip edges and the inner lip edges of the adjacent pipe wall arc plates are clamped, and the pipe wall arc plates are clamped so as to form an integrated round pipe; a group of vertically opposite pipe wall arc plates are provided with symmetric opposite handles, and the handles are fixed with the pipe wall arc plates through connecting plates; each pipe wall arc plate is in the shape of a 1/4 arc, and the connecting plates are fixed on the inner sides of a group of opposite inner lip edges; the connecting plates and the pipe wall arc plates are equal in length, the handles and the connecting plates are equal in length, and the two ends of the handles are provided with semicircle arc surfaces. The sizing inner pipe provided by the invention is used for supporting the paper pipe inside in a paper pipe rolling process, and after the rolling of the paper pipe is finished, the sizing inner pipe is disconnected and taken out from the paper pipe, so that the abrasion of the inner surface of the paper pipe is small, and the inner surface quality of the paper pipe is guaranteed.