Abstract：With the resources exhaustion of medium-sized thickness and thick coal seam，more than 10 mines will be transferred to the lower coal group in Lu¢an Group. The occurrence mode of coal seams #15–1 and #15–3 in the lower coal group is thin coal seam group with average distance 4.4 m. Therefore，the conventional staggered distance model of ultra-close thin coal seam group during combined mining is put forward；and the theoretical research and physical simulation are carried out. The conventional staggered distance formula is proposed. To avoid interaction between the roof periodic caving of coal seam #15–1 and the leading effect of coal seam #15–3 in mining，from the point of safety，the conventional staggered distance is confirmed as 1.3–1.5 times of the roof periodic caving span of coal seam #15–1. Combined with the experimental results，the conventional staggered distance is determined as 17.5 m. Physical simulation test results show the feasibility of the conventional staggered distance in combined mining. In addition，the elevation reason of several measuring points on the top of the working face near coal seam #15–1 is analyzed；and the roof subsidence phenomenon，which has mainly two major changes during the course of working face advance，namely，the roof caving in the stoping course of upper and lower working faces，is summarized，especially the roof caving of lower coal seam which will have larger influence.
