The invention provides a chipless reducer pipe cutting machine, comprising pipe support frames, a clamping mechanism, cutting blades and a drive device. The cutting machine is arranged on the hollow part for placing the pipes to be cut. The clamping mechanism is arranged on the outer surface of the pipe. The pipe support frames comprise two parts which are respectively arranged at the two ends of the clamping mechanism. The cutting blades are arranged at one side of the clamping mechanism. The cutting machine is also provided with linear displacement sensors for automatically adjusting the positions of the cutting blades. The cutting machine is easy to operate and can correspond to various specifications, lower the cost and ensure cutting to be more stable and the cut to be flatter and smoother.