Clamping device in pipe cutting machine

The utility model discloses a clamping device in a pipe cutting machine. When a pipe is clamped, the pipe cannot be deformed, and is clamped firmly. The clamping device comprises a guide rail, two opposite clamps are arranged on the guide rail in a sliding mode, each clamp comprises a support arranged on the guide rail in a sliding mode, hollow main shafts are rotatably arranged in the supports, one ends of the main shafts stretch out of the supports and are provided with flange plates, and a circle of clamping jaws which can respectively move in the radial direction of the flange plate and are used for expanding the pipe is arranged on each flange plate. The clamping device has the advantages that the pipe is fixed in an expansion mode, and the pipe can be prevented from being deformed when the pipe is fixed.