In view of the problem of reasonable width of coal pillar in the working face section under the condition of thick hard rock formation, No. 63 upper 06 Face of Dongtan Mine was taken as the engineering background, the reasonable width of the coal pillar in the working face section under the condition of thick hard rock formation was studied by the FLAC3D numerical simulation software analysis method, and the reasonable size of the small coal pillar was revealed. The results of the study showed that: ① When the coal pillar width was small, the displacement difference between the coal wall and the center of the coal pillar was relatively small, but the overall displacement was large, and the stress was borne by the entire coal pillar. In contrast, when the coal pillar width was large, the displacement difference between the coal wall and the center of the coal pillar was significant, but the overall displacement was small, and the stress was borne by the coal wall. ② When the coal pillar width was small, although the units in the coal pillar may experience damage, the coal pillar did not undergo significant deformation and maintains good support. However, as the coal pillar width increased, stress concentration areas began to appear within the coal pillar, with vertical stress gradually increasing. Moreover, the significant stress retained within the coal pillar cannot be transferred to the solid coal seam. ③ Under the conditions of thick and hard rock layers, the reasonable width for the retained coal pillar should be in the range of 5 to 7 meters. Setting a reasonable width for the small coal pillar not only improved the coal extraction rate but also played a certain control role in the deformation of surrounding rock in the roadway, ensuring the safe and efficient mining of coal mines. The research findings offered references for determining the appropriate coal pillar width in working face sections under conditions of thick and hard rock layers in similar geological contexts.