In a cylinder dividing mechanism of a pneumatic tool, the first and second air pressure driving spaces are formed in the chamber, the first and second external channels are set externally on the circumferential wall, the first external channel is connected with the first air intake and air intake/exhaust dividing controller, and the second external channel is connected with the second air intake and air intake/exhaust dividing controller. As such, a single chamber is provided with two air pressure driving spaces for synchronous compression and driving of the rotor. The driving torsion for the pneumatic tool could be multiplied without need of increasing the volume of the chamber of the cylinder to cater for the need of the users with improved applicability.