<p>The shear mechanical behavior of joint surfaces is crucial for the safety and stability of rock engineering. Under constant normal load (CNL) conditions, the boundary element method is employed to calculate the distribution of normal contact forces. By combining the “dip angle” with the Patton model, a shear force calculation program analyzes the shear results for each discrete element. This approach allows for the investigation of microscopic phenomena during the shear process and provides insights into the effects of variations in load and shear displacement. Changes in load and shear displacement influence both the shear forces and the shear zones. The shear zones primarily expand and contract around their original regions. At local points of fracture shear, the patterns of shear force exhibit a differential effect, indicating that regions with higher shear stress are more prone to shear failure. This study provides a reference for understanding the variation of shear forces and shear zones during the shear process and offers a new perspective for investigating the mechanisms and patterns of shear failure.</p>