To ensure the coal mining safety, drilling with large diameter in gas formations and then discharging gas by draining through borehole in gas rich formations, the non-balance drilling conception was used. In allusion to the problems existing in using medium pressure air as drilling fluid under the conditions of breccia formed by small structural action, loose coal layer and unstable formations, new type of drilling tools and bits was designed. The mechanism of cutting removal by air media was stated and analyzed. Meanwhile, the problems occurred in practices and their resolving methods were concluded.