A direction-switchable pneumatic cylinder includes: a cylinder body with two intakes, several exhaustion ports and a rotary shaft; and a predetermined number of movable wheels and fixed wheels arranged in the cylinder body and interlaced with each other. Each of the movable wheels and fixed wheels is formed with several vents concentrically arranged into an inner circle and an outer circle. The rotary shaft is fitted through the movable wheels and fixed wheels. The fixed wheels are not rotatable, while the movable wheels are synchronously rotatably with the rotary shaft. The outer circles of vents of the fixed wheels and the movable wheels are aligned with one intake, while the inner circles of vents of the fixed wheels and the movable wheels are aligned with the other intake. When high-pressure gas is guided into the pneumatic cylinder from one intake, the airflow will flow through the outer circles of vents to drive the movable wheels and the rotary shaft in one direction. When high-pressure gas is guided into the pneumatic cylinder from the other intake, the airflow will flow through the inner circles of vents to drive the movable wheels and the rotary shaft in another direction.