Abstract: According to the sectional coal pillar rational width applied, mining dynamic influence scope determination and other problems occurred in a face to face construction process of fully- mechanized top coal caving mining face and a mining gateway in ultra thick seam of Tashan Mine, the theoretical analysis, numerical simu lation, site stress measurement and other means were applied to study the breaking structure of an overburden strata, stress distribution of the sectional coal pillar and rational width of the sectional coal pillar. The stress in one side of the coal seam in the goaf had a serious influence scope of 30 ~ 35 m. The site measurement of the C oal pillar stress showed during a mining period of an adjacent coal mining face, along the coal pillar width, the stress was in a unimodal asymmetric distribution, stress peak zone had a distance of21 ~ 30 m to No. 8210 air retuning gateway and had a distance of 8 ~ 17 m to No. 8208 goaf and the roof movement in the goaf was stabili zed with a delay distance of over 120 ~ 130 m. The study results showed that under the condition of the face to face to construction of the fully- mechanized top coal ca ving mining face in ultra thick seam of Tashan Mine, the coal pillar with a set width of 38 m was safety and the coal pillar width could be reduced to 30 ~ 32 m from a vie w of the coal pillar stress distribution.