Abstract: Steeply inclined thick coal seam is a very special coal seam occurrence condition and the particularity of the mining methods determines the efficiency of coal mining, the stress evolution regularity of coal and rock mining process is a good way to reveal mechanism of disasters and so on steeply inclined thick coal seam mining way and to study the stress evolution regularity of coal and rock is very necessary. Based on COMSOL Multiphysics numerical simulation software, this paper conducted numerical simulation research on the stress evolution law of rock mass and coal body under the condition of horizontal subsection mining of 45# steeply inclined extra-thick coal seam in Wudong Coal Mine. The research results show that: (1) After the horizontal subsection mining of coal seam, the stress of rock strata near the roof of coal seam is large, and that near the floor of coal seam has little change. The stress variation range of overburden displacement stability shows the shape of "funnel". (2) The phenomenon of stress concentration occurs in the local area of overburden, and a circular "stress concentration circle" is produced. The size and shape of the "stress concentration circle" change with the mining of coal seam, and the phenomenon of stress concentration is gradually weakened. (3) The stress concentration of coal in working face is mostly distributed in the coal near the roof, while the stress concentration degree of coal near the floor is smaller than that of the roof. (4) The axial stress distribution of working face can be divided into three zones: plastic zone, elastic zone and original rock stress zone. The lateral stress of coal body along the strike direction decreases with the increase of distance from working face.