Abstract: In order to determine a rational width of the sectional coal pillar in fully mechanized coal mining face in seam closed distance to below seam in Mugua M ine, based on the mine pressure and strata control theory, a mechanics model of a broken delta block structure in lateral strata was established.The cracking length of t he main roof along the coal mining face forward direction and the lateral cracking span calculated was 11.9 m individually.The cracking location of the delta block struct ure in the coal seam was 11.5 m.Meanwhile the numerical simulation method was applied to establish a 3D mechanics model of the coal mining face.With the coal mini ng face moving forward, the lateral support pressure peak of the gateway was 20 MPa, the max stress concentrated was 2.55 and the plastic zone was about 10 m.The site detection showed when the rational width of the sectional coal pillar was 16~18 m, the mining gateway would be less affected by the mining operations of the fully mechanized coal mining face.