Abstract: Increasing the upper operating pressure is the most direct, effective and comprehensively beneficial solution to increase the working gas volume of the reservoir. This paper quantitatively evaluates the operating cap pressure and reservoir capacity of the 1-29 reservoir in Nambourg field, Jidong, on the basis of the in situ measured minimum principal stress in the mine wells, and the results show that: based on the minimum principal stress criterion, the cap pressure corresponding to the occurrence of tensile damage in the cap layer is the lowest, i.e., based on the measured minimum principal stress, the operating cap pressure of the 1-29 reservoir in Nambourg field is determined to be 27.20 MPa. effective reservoir capacity calculation model, taking into account the water content, residual water and edge porosity of the gas layer, the wave coefficient of the oil layer, the efficiency of the gas drive fluid and the utilization rate of the oil-bearing space, etc., the upper limit pressure is raised from the original formation pressure of 22.50 MPa to 27.20 MPa, and the effective reservoir capacity of the reservoir is increased from 15.46×10⁸ m³ to 18.14×10⁸ m³, with an increase of the capacity of the reservoir of about 17.3%, which is expected to significantly improve the economic benefits of the gas storage reservoir, and the results of this paper have certain reference value for the quantitative evaluation of the upper pressure limit and reservoir capacity of other underground gas storage reservoirs.