Abstract: In the light of the fact that many underground mine fields are damaged by small coal mines，and in order to avoid serious damages to the limited coal resources，a secondary mining technology after backfilling was put forward based on building a key bearing layer in the failure area of small coal mines.The mechanical model of roof caving impacting on key bearing layer in destruction area was built，and the determining method of the thickness of key bearing layer in the failure area，the choice of backfilling materials，and the layered backfilling method were investigated respectively.The results showed that the key bearing layer with less than 5 m in thickness can ensure the stability of both roof and the coal walls in secondary mining of Pingshuo second coal mine.Inorganic materials were filled in failure areas of the small coal mines by levels to form cutting layer and key bearing layer with different strength，which made them meet the mining requirements of the normal coal seam and reduced the cost.The research results are of great theoretical and practical significance for the coal seam with similar conditions.

Key words: Failure area of small coal mines, Secondary mining with backfilling, Key bearing layer, Artificial roof, Layered backfilling method