Abstract: To elucidate the damage evolution law of coal pillars in gob−side entry driving and determine their optimal width, this study took the 311304 working face of Bayangol Coal Mine as the engineering background, aiming to addressed the key technical challenge of balancing roadway stability and coal resource recovery efficiency. As a critical design parameter, coal pillar width directly governed surrounding rock control effects and mining safety, making systematic research essential for on−site engineering guidance. Methodologically, the Rock Quality Designation (RQD) classification method was first employed to characterize in−situ rock stratum parameters, providing a reliable basis for numerical simulations due to its standardized reliability in evaluating rock mass integrity. To ensure parameter accuracy, uniaxial compression tests were conducted on field−collected coal and rock samples to calibrate their mechanical properties, aligning simulations with actual conditions. Subsequently, a UDEC−Trigon discrete element model with a local grid resolution of 0.4 m was established. Leveraging the discrete element method's strength in simulating discontinuous rock mass deformation, the high−resolution grid effectively captured fine−scale coal pillar damage, enabling comprehensive analyses of damage evolution and surrounding rock control effects for coal pillars of varying widths. The results show that coal pillar width exhibits a significant negative correlation with overall damage rate and bearing capacity. As width decreases, the overall damage rate rises continuously, and high−damage zones on both sides of the pillar gradually converge. When width is less than 6 m, the coal pillar suffers severe structural deterioration with extensive interconnected fractures, leading to a drastic drop in bearing capacity that fails to resist surrounding rock pressure, resulting in uncontrollable roadway deformation. In contrast, coal pillars ≥6 m retain a relatively intact low−damage core in the center, which acts as the primary load−bearing structure, inhibiting fracture propagation and confining roadway deformation within controllable limits. Thus, the optimal coal pillar width for the 311304 working face is determined as 6 m. Field measurement data validate the simulation results: after constructing the gob−side entry with a 6 m−wide coal pillar, monitoring of surrounding rock displacements, coal pillar stresses, and support stability confirms effective suppression of deformation and failure. No excessive deformation, roof collapse, or pillar instability occurred during service, fully guaranteeing roadway stability and operational safety. This study provides a scientific basis for coal pillar design in the 311304 working face and valuable technical references for similar projects in coal mines with analogous geological and mining conditions.