The invention relates to a tube part cutting device. The tube part cutting device comprises a rack and a worktable, wherein an air cylinder is arranged on the rack, a sliding plate is slidably connected in the air cylinder, a connecting rod is fixed to the sliding plate, a fan-shaped gear is rotatably connected to a second supporting plate on the rack, and the end, far from the sliding plate, of the connecting rod is rotatably connected to the fan-shaped gear; a supporting roller is rotatably connected to the worktable, a clamping gear is also rotatably connected to the worktable, a through hole is formed in the middle of the clamping gear, a stretchable driving gear is arranged on the clamping gear, the driving gear is fixedly connected to a leaning rod, a telescopic spring is arranged inthe driving gear, a vertical plate is also fixedly connected to the worktable, a rack is slidably connected to the vertical plate, a first grinding tooth part and a second grinding tooth part are arranged on the rack, a transverse plate is fixedly connected to the vertical plate, a cutter bar is fixedly connected to the transverse plate, a tool bit is arranged at the bottom end of the cutter bar,a gas guide pipe is arranged in the cutter bar, an air jet hole is formed in the cutter bar, and an air outlet pipe is connected between the gas guide pipe and the air outlet. The tube part cutting device provided by the invention solves the problem that the cutting section of a tube part is irregular.