Abstract: Using the FLAC numerical simulation and 1:200 similar material simulation, the paper analyzes the stress field and the changing law of the displacement field which belongs to the open-air side slope around the pressing foot of backfilling internal dumping and the well labor tunnel surrounding rock under this side slope in detail, and analyzes the influence to the stability of the side slope and tunnel with the different backfill heights with emphasis. The findings indicates that after backfilling to the +1358.8m the tunnel destruction area is no longer to connect with the front virgin coal destruction area, and after backfilling to the +1393.6m the reducing scope of the side slope and tunnel's horizontal displacement surpasses 60%, meanwhile the attenuation proportion of the supporting capacity of the virgin coal is reducing obviously.