Abstract: [Objective]The stability coefficient is a critical metric for assessing rockfall hazards. Traditional two-dimensional (2D) cross-sectional models, which fail to account for three-dimensional (3D) geometric characteristics and the synergistic effects of multiple fractures, often result in substantial errors in the calculation of stability coefficients. [Methods]In this study, a 3D stability calculation model for translational rock masses with a steeply dipping fracture at the rear edge was developed based on the theory of limit equilibrium. Additionally, a method for synthesizing the water pressure vectors of multiple fractures and an algorithm for calculating the buoyant force on the sliding surface were proposed. The model was applied to the Dazhaikou rock mass in Fuling District, Chongqing, and the differences between the 3D and 2D model calculations were compared and analyzed. [Results]The results indicate that the 3D model can accurately characterize the irregular geometry of the rock mass and the hydro-mechanical coupling effects of multiple fractures. Under heavy rainfall conditions with both fractures filled with water, the stability coefficient calculated using the 3D model is 5.5% lower than that obtained from the 2D model. Numerical simulation validation demonstrates that the discrepancy between the 3D limit equilibrium method and the strength reduction method is less than 0.4%. [Conclusion]The study concludes that the shape of the rock mass significantly influences its stability. Except for regular cubic shapes, a 3D analysis method is generally necessary to ensure the accuracy of the assessment in most cases.