Abstract: The district sublevel coal pillar has a significant impact on the hydraulic connection between adjacent goaf. However, in the design of underground reservoir in coal mine, the determination of district sublevel coal pillar parameters lacks scientific theoretical support. In view of the above problems, the coal pillar in section 4-2 coal panel of Wanli No.1 Mine was taken as the research object, according to the evolution law of side abutment stress of district sublevel coal pillar, the seepage experiment of coal (rock) sample was designed, the variation function of permeability of coal (rock) sample with vertical stress was obtained, and the distribution law of porous medium permeability in goaf was revealed. On this basis, the CFD numerical calculation of water seepage characteristics of district sublevel coal pillar was carried out. The research results show that with the decrease of water level in goaf and the increase of coal pillar width, the flow range and velocity of water in goaf decrease continuously, under the condition of water level of 18.65 m, 28.65 m and 38.65 m, the critical coal pillar width of goaf water entering adjacent goaf is 30 m, 50 m and 70 m respectively; when the district sublevel coal pillar width is less than 10 m, the water in goaf can bypass the elastic core zone in the bottom coal seam and enter the adjacent goaf; when the width of coal pillar exceeds 20 m, the goaf water cannot enter the adjacent goaf through the bottom coal pillar.