Abstract: Abstract: According to the inclined coal seam downward mining goaf digging roadway coal pillar size selection problem, this paper takes the responsibility of building coal 7259 airway as the background, using numerical simulation method to simulate the size of coal pillar from 3m to 10m roadway surrounding rock stress field and displacement field. The research results show that: 5m coal pillar width vertical force and peak has become stable, coal pillar exists some of the width of the elastic core, can bear induced by coal mining of abutment pressure of roadway influence. At this point, the displacement of the horizontal direction and the peak value of the horizontal displacement of the coal pillar is decreased, and the displacement of the middle level of the coal pillar is slower. The final determination of reasonable coal pillar size is 5m. Then, the size of coal pillar is calculated by theoretical analysis. The results of the two methods are quite different. The research results are used in the field practice, the deformation of the roadway surrounding rock is effective, and the maintenance effect is good.