Abstract Large-diameter pressure relief boreholes are one of the primary measures for preventing coal mine rockburst. However, the implementation of these boreholes disrupts the original support structure of the roadway surrounding rock, leading to conflicts with surrounding rock control. Therefore, the pressure relief and energy dissipation behavior of variable-diameter boreholes in roadway surrounding rock was studied. Using a typical rockburst-prone coal mine as the engineering background. Based on elastic–plastic mechanics theory, the elastic solution for the stress distribution around the borehole and the extent of the pressure relief zone are analyzed. Numerical simulation software was used to study the effects of variable diameter drilling parameters (deep reaming diameter, deep reaming depth, and deep reaming spacing) on the pressure relief of roadway surrounding rock, energy dissipation in the roadway, and roadway deformation. The research results indicate that the distribution range of the pressure relief zone is influenced by the vertical stress, lateral pressure coefficient, cohesion, and internal friction angle of the coal body. The maximum radius of the pressure relief zone increases with the borehole diameter. As the deep reaming diameter increases and the borehole spacing decreases, the stress concentration in the surrounding rock of the roadway shifts more significantly toward the deeper region, making it easier to form a dual-peak stress zone. This enhances the pressure relief and stress transfer effect on the surrounding rock of the roadway, leading to greater energy dissipation. From the perspective of energy dissipation, it is concluded that the optimal location for the variable-diameter borehole should be within the peak vertical stress zone of the surrounding rock that has not been relieved. This study provides guidance for the prevention and control of dynamic disasters in deep coal and rock.