ABSTRACT Conventional triaxial compression tests were conducted on shale specimens under varying initial prestress conditions to investigate their mechanical properties and energy evolution characteristics, thereby revealing the shale damage mechanism. The results demonstrate that the peak differential stress of the shale samples increases with the rising initial prestress, following an exponential function. Based on the maximum and minimum principal stress data of the shale samples and the Mohr‐Coulomb criterion, the cohesive force and internal friction angle of the tested shale were calculated as 29.86 MPa and 38.92°, respectively. By analyzing the ultimate storage energy of shale samples under different confining pressures, it was found that the ultimate storage energy increases exponentially with confining pressure. Additionally, the dissipated energy at peak stress exhibits a linear relationship with increasing confining pressure. This study provides critical insights into the damage mechanisms of shale under complex stress conditions and offers theoretical support for optimizing shale gas extraction engineering practices. The quantitative relationships between stress, energy evolution, and confining pressure contribute to improving the efficiency and safety of shale reservoir development.