Abstract: To fully grasp the dynamic pressure variations during gas injection of underground gas storage (UGS) and resolve the difficulty in determining formation parameters caused by continuous gas injection, an integrated calculation method of pressure and formation parameters in gas injection process of UGS was developed according to on-site static and dynamic data. The method was based on an improved particle swarm optimization (PSO) algorithm and integrated the calculation methods of reservoir pressure, bottom-hole pressure, and wellhead pressure. The wellhead pressure was first calculated by these calculation methods, and improved PSO algorithm was then employed to continuously adjust and optimize pressure and formation parameters. In this way, the obtained wellhead pressure could be fitted with measured wellhead pressure to the optimal extent, which could further lead to the determination of formation parameters such as reservoir pressure, bottom-hole pressure, average permeability of reservoirs and investigation radius. The integrated method was used to calculate the wellhead pressure of three injection and production wells and the average permeability of reservoirs. The results show that the determination coefficients for calculated and measured wellhead pressure of the three wells were 0.9889, 0.9893, and 0.9784, and the calculated reservoir permeability was consistent with that obtained from well test interpretation. This indicates that the developed method can produce reliable results. The research results demonstrate that the integrated method can be used to learn the pressure variations during the gas injection process of UGS and is conducive to guiding the safe operation of UGS.