The invention provides a machining tool for cylindrical workpieces. The machining tool comprises a bottom plate, a fixed support, a movable support, a first sliding groove, a fixed roller carrier, a sliding roller carrier, rollers, a first air cylinder, a second air cylinder and a locking bolt. By the adoption of the rollers, rapid workpiece clamping and accurate centering can be achieved, and workpieces can rotate conveniently in grinding or turning or welding or the like. By the adoption of the action of the air cylinders, automatic workpiece clamping can be achieved. By the arrangement of the first sliding groove and a second sliding groove, the distance between the fixed support and the movable support and the distance between the sliding roller carrier and the fixed roller carrier can be adjusted according to needs so that workpieces of different diameters can be clamped or different portions of workpieces can be clamped, and accordingly the universality and reliability of the tool are improved. The machining tool for the cylindrical workpieces is high in automation degree and clamping efficiency, greatly shortens the workpiece machining period, improves productivity and lowers the production cost.