Abstract: The reservation of small coal pillars in roadway excavation along goaf under deep mining conditions of thick coal seams is an effective way to reduce resource loss caused by wide coal pillar protection. However, the high stress concentration and mining-induced disturbance caused by the reduction of pillar width remain significant. It is therefore necessary to comprehensively consider the strength characteristics of coal pillars, the changes in the bearing stage, and the influence of pressure relief by roof cutting on the development of the plastic zone to determine a reasonable width for small coal pillars. Taking the roadway excavation along goaf with reserved small coal pillars in a certain coal mine as the engineering background, the width of the internal plastic zone of the coal pillar was calculated based on an ideal elastic-plastic constitutive model considering the residual strength of coal, and the variation of the plastic zone in coal pillars with different widths before and after pressure relief by roof cutting was analyzed. The results showed that the expansion of the plastic zone in small coal pillars was the most significant during the working face mining stage. The width of the plastic zone first increased and then decreased with the increase of coal pillar width. Pressure relief by roof cutting significantly reduced the width of the plastic zone, with a maximum reduction of 43.2% compared with that without pressure relief by roof cutting. Under the condition of pressure relief by roof cutting, the plastic zone in a 5 m-wide small coal pillar accounted for only 46.7% after mining, leaving more than half of the elastic zone for bearing, and the reasonable width of the small coal pillar was determined to be 5 m. On this basis, a numerical simulation of the 5 m-wide small coal pillar under pressure relief by roof cutting was carried out. The results showed that compared with the condition without roof cutting, the peak vertical stress inside the coal pillar decreased by more than 36%, the maximum deformation of the roof and floor decreased by 8.4% and 9.8%, and the maximum deformation of the pillar rib and solid coal rib decreased by 48.8% and 46.7%, respectively. Industrial test results showed that under pressure relief by roof cutting, the convergence of the roof-floor and ribs of the roadway with a 5 m-wide coal pillar decreased by more than 52% and 63%, respectively, compared with that without roof cutting, ensuring the safe and efficient mining of the working face.