A compact one touch pneumatic wrench includes a cylinder having an improved air passage to achieve one touch function and a housing mad of engineering plastic material. Compared to a conventional pneumatic wrench which needs one hand to hold the handle and the other hand to operate the clockwise/counterclockwise rotation of the motor, the present invention improves the air passage of the cylinder to provide a simple and convenient operation with only one hand, providing a convenient operation and enhancing the work efficiency.