Abstract: [Objective] The Biot coefficient is defined as the ratio of the change in pore volume to the change in total rock volume, reflecting the efficiency with which pore pressure offsets externally applied total stress under loading conditions. As a key parameter in poroelastic theory, the Biot coefficient couples pore pressure with effective stress in the reservoir and plays a critical role in geostress calculation and wellbore stability analysis. [Methods] In this study, based on the equivalent inclusion theory, parameters such as the polarization factor and fracture aspect ratio are introduced to characterize the influence of fracture geometry on reservoir mechanical properties. In conjunction with the Griffith fracture criterion, a method for determining the expected aspect ratio of fractures is developed, leading to analytical expressions for the Biot coefficient in both fractured reservoirs and dissolution cavities reservoirs. [Results] The results show that the maximum errors in the calculated maximum and minimum horizontal principal stresses using the proposed Biot coefficient method are 5.75% and 6.03%, respectively, compared with field-measured geostress data, meeting engineering accuracy requirements. [Conclusion] These findings provide a theoretical basis for accurate characterization of the geostress field and efficient exploration and development of unconventional reservoirs.