Abstract: In order to explore the reasonable coal pillar size of the backfilling working face, taking Shandong Yineng Coal Mine as the engineering background, a structural mechanics model of “backfilling body-coal pillar-backfilling body” was constructed. The damage level is determined by studying the internal failure conditions under different sizes of coal pillar, and the bearing characteristics of coal pillar in different sizes, zones and grades are proposed. The vertical stress, plastic development characteristics and deformation of coal pillar at different scales of 10 m, 6 m, 3 m and 1 m are simulated and analyzed by using UDEC software. The simulation shows that the vertical stress distribution decreases with the decrease of width, the minimum reaches 16.5 MPa, the plastic zone increases with the decrease of coal pillar size, the deformation of coal pillar increases with the decrease of coal pillar width, and reaches the minimum deformation at the range of 3-6 m; according to the “quadrant method” of coal pillar stress and deformation characteristics, the coal pillars stability of different widths was explored. Combined with the safety and economic factors of the mine, the reasonable width of small coal pillar under the conditions of superhigh water backfilling mining is determined to be 3 m. It is proposed to maintain the stability and sealing of small coal pillar by grouting and plugging, anchor bolt and mesh support technology, and determine the grouting process, materials, timing, pressure and other parameters, which could provide an effective guarantee for the safe and high recovery rate for backfilling mining with deep buried depth.