Abstract: Pressure in wellhead is an important parameter for gas-cutting two-phase flow fields of well bore by air drilling.Two-dimensional flow fields in well bore were simulated using finite volume method on a multi-block structure grid system.Distributions of velocity and pressure along the depth of well were obtained.Combined with the minimum velocity of carrying cuttings and critical erosion velocity,reasonable value range of pressure in wellhead was got.The results are in good agreement with the actual operating parameters.