Air drilling is a drilling technology which uses air as the recirculated medium. There are many differences in the pressure distribution of circulatory system, the choice of drilling machinery and the configuration of drilling parameters between air drilling and other conventional drilling technologies. In this paper, we mainly focused on the force analysis and mechanism of rock chip in air drilling, and then did a simulation experiment to achieve the minimum injection gas of annular drilling with the CFD software under the condition of without entrance pressure.