In the shale gas reservoir of the Qianfoya Formation in the east-west syncline of Puguang in northeastern Sichuan, overpressure is prevalent.The distribution range, genetic mechanism, and pressure evolution process of the overpressure storage box have not been fully clarified. Based on geological data and logging data, the paper comprehensively analyzes the distribution range, genetic mechanism, and pressure evolution process of the pressure storage box in the first section of Qianfoya Formation shale gas reservoir using the Eaton method, Bowers method, fluid inclusion technology, and basin simulation technology. The results show that: ① The upper floor of the first section of Qianfoya Formation shale gas reservoir is composed of the Daanzhai Member and the bottom of the first section of Qianfoya Formation, consisting of sandy tuffaceous sedimentary tuff, tuffaceous anisotropic quartz sandstone, tuffaceous siltstone, and mudstone. The roof was mainly composed of mudstone interbedded with tight sandstone in the ④ and ⑤ sub-layers of the first section of Qianfoya Formation. Good roof, floor and lateral partition layers avoid the loss of natural gas; ② The overpressure source was mainly caused by fluid expansion due to hydrocarbon generation, followed by structural compression, with a weak relationship with uneven compaction; ③ The abnormal pressure storage box has undergone a stage of organic matter immature-low mature normal pressure, organic matter mature liquid hydrocarbon overpressure stage, organic matter high mature-overmature shale gas abnormal pressure stage, late-stage extrusion and pressure increase and uplift pressure relief collaborative transformation and finalization stage.