Abstract: Accurate calculation of the bound water saturation, combined with the "dual saturation" method of water saturation can more effectively evaluate whether the reservoir is a pure oil and gas layer.In this paper, the relationship between the bound water saturation and the porosity with the height of the hydrocarbon column is analyzed by the core capillary pressure experimental data. When the porosity is certain, the bound water saturation is reduced exponentially with the increase of the height of the gas column.When the the height of the oil and gas column is certain, the bound water saturation decreases with the increase of the porosity. On the basis of this study, the bound water saturation of the gas layer in the bottom water gas reservoir is determined by J-function average method. For the gas reservoir without gas water interface, the bound water saturation can be determined by establishing the NMR bound water saturation and porosity model. The practical application shows that the research method applied in this paper is accurate and reliable in calculating the bound water saturation, which lays a foundation for the identification and quantitative evaluation of reservoir fluid properties in X-X gas field of Yingqiong basin. It has certain reference for the logging evaluation of complex fluid properties in other basins.