Abstract Pore overpressure is widely developed in Paleogene strata of Bohai Bay. It is traditionally believed that overpressure in this area is caused by unbalanced compaction of thick mudstone and hydrocarbon generation of organic matter. By using Eaton formula to calculate an exploration well that encountered overpressure in the strike-slip fault zone in the northern Bohai Bay, it is found that the formation overpressure at the location of the well is contributed by other overpressure factors. The possibility of overpressure caused by hydrocarbon generation is excluded from geochemical analysis. Based on the structural style and plane fracture system morphology in the seismic data volume, it is inferred from the perspective of structural kinematics that the formation at the location of the well is subjected to compression stress, and it is considered that the formation overpressure in this area is the result of unbalanced compaction of mudstone and tectonic compression. In this study, formation overpressure based on tectonic compression was found in the s-type strike-slip fault zone in the Bohai Bay, and the exact distribution position of the overpressure development zone in the s-type fault zone was pointed out. This discovery will attract attention to the study of formation pressure in the s-type fracture area, thus ensuring drilling safety.