Abstract: A torsion detecting mechanism for a pneumatic tool is a torque detecting mechanism which comprises a rack, a driving device, a buffer device, a sensing member and a pressure relieving device. The rack is provided for mounting the driving device, the buffer device, the sensing member, and the pressure relieving device. A pneumatic tool drives the driving device to rotate, such that the buffer device is pressed against the sensing member to obtain the test data, such as the torque of the pneumatic tool. After the test is finished, the pressure relieving device will relieve the oil pressure of the buffer device, enabling the driving device to be immediately returned to the state of waiting for the next test. Thereby, such arrangements not only provide a stable test, an accurate test data, and a high test safety, but also can wide the industrial application.