Porous media containing water is the prerequisite of existence of threshold pressure gradient (TPG) for gas flow. Based on theory of fluid mechanics in porous medium considering TPG, the non-Darcy flow mathematical model is established for formation pressure analysis of water-bearing tight gas reservoirs. It could provide semi-analytic solution of unsteady radial non-Darcy flow. According to the solution of unsteady radial non-Darcy flow, an easy and accurate calculation method for formation pressure analysis is presented. It can provide theoretical foundation for development design of water-bearing tight gas reservoirs. The analysis of calculation results demonstrates that the higher TPG is, the smaller formation pressure of water-bearing tight gas reservoirs spreads. In the same output, the reservoir sweep of non-Darcy gas flow is larger than that of non-Darcy liquid flow. And the pressure drop near wellbore is smaller than that of non-Darcy liquid flow, which is different from Darcy flow.