Abstract: Pneumatic DTH drilling technology has been widely applied because of its advantages of fast drilling speed, obvious anti-slant effect and environmental protection, but, DTH hammer is unable to carry out reverse reaming. According to the possible blockage, a back reaming device which is suitable for φ311.2 mm pneumatic DTH hammer was innovated. Meantime, the operation flow and precautions of back reaming were developed by using this device. The field application shows that this device can effectively reduce blockage risk of air drilling, shorten drilling cycle and save cost.