The calculation of gas injection displacement of air drilling methods is mainly by the minimum kinetic energy and the minimum rate law; the paper analyzes these 2 methods, the minimum kinetic energy method was optimized and the injection volume requirement for the hole of 81/2in with different depth were calculated. Analysis was made on the factors affected the gas drilling equipment configuration, and the configurations under different condition were finally determined, which could be the scientific basis for economic construction of gas drilling.