Abstract: Taking Xingshan Iron Mine as research background，combined with the actual situation of the mine，and based on the covering layer structure optimization theory of random media ore-drawing theory and natural grading theory of covering layer backfill from open pit to underground，the covering layer thickness of Xingshan Iron Mine is determined to be 45 m and the forming method is high step once dumping，which meet the safety functions of the anti-dilution losses，anti-rockburst，blocking water，reducing air leakage for cold proof，and forming the extrusion blasting and the end ore-drawing conditions.A detailed program and the technical guarantee measures are proposed.The main conclusions are as follows：①Xingshan Iron Mine overlay layer have overall downward layer and flowing layer.The waste rock backfill size at flowing layer is not less than 20 mm，rock content of 100 mm or above is not less than 40%，and the thickness is not less than 20 m.②The waste rock backfill size of overall downward layer is smaller than 5mm，and has a ratio of 3∶7 with that of greater than 5 mm.Its thickness is not less than 25 m.After the implementation of covering layer，Xingshan Iron Mine owned good evaluating index in the leakage rate，ore dilution rate，underground landslides and seepage time and other indicators.The research provides a guiding reference for similar mines.

Key words: Transition from open pit to underground, Covering layer, High bench tipping, Natural classification