Tight and shale gas reservoirs are characterized by pores in the range of micro- and nanometer. The description of the gas flow in such tight porous media is complicated by the coexistence of various flow regimes. Generally, porous media is represented by a bundle of tortuous capillaries and contributions of various flow regimes are incorporated by numerical integration of the flow rate of individual capillary, which causes inconvenience for practical application. In this paper, approximate expressions for apparent gas permeability of tight porous media with a relative error less than 0.1 based on the lognormal pore size distribution and the fractal pore size distribution have been separately derived. With the proposed expressions, apparent gas permeability of tight porous media can be calculated without numerical integration. The proposed method has been validated by published data.