Abstract: The room and pillar mining was used at 3^-2 coal seam before Tanggonggou Coal Mine technological improvement. When the 4^{-2 upper} coal seam is mining, the corresponding area of roof will be affected by 3^-2 coal seam goaf pillar and produces stress concentration, which is easy to cause rib spalling, roof fall, workface coal wall rib spalling in 4^{-2 upper} coal seam roadway. According to UDEC numerical model, this paper studies the 3^-2 goaf legacy pillar domino instability phenomenon with the advancing of 4^{-2 upper} coal seam workface, analyzes and obtains the workface displacement change laws in 4^{-2 upper} coal seam and the effect of different widths of coal pillar on domino instability phenomenon.