Abstract: Facing with the complex mined-out area of open pit，a three-dimensional shape of the mined out area was obtained through drilling and laser scanning.Combined with the researches on the safe roof thickness of the mined-out area in Yuanjiacun Iron Mine，the optimum occasion for treatment was determined to open up free space for the mined out area in overall drifting progress.Taking a large，complex，layer-distributed mined out area group No.25 of Yuanjiacun Iron Mine as a case，the explosion of once pore-forming at full height，zoning and layering is adopted.Interaction between the upper and lower blasting layers，and the lower layer firstly blasts of pillar 25-2 at mined out area，can enlarge the exposed area of the lower mined out area and results in the failure of the mined-out area.The lower layer collapses and then fills the gob as a blasting funnel.The centre cutting effect could create lateral free space，enhance energy efficiency and improve explosive effect.The geometric center of the upper blasting layer near the mined-out area roof acts as the initial explosive point，and the combined effect of radial extrusion explosion and the blasting funnel within the upper layer could apply a secondary impact on the lower basting layer and promote the collapse and filling of the mined-out area，with the desired results achieved.

Key words: Drilling, Three-dimensional laser scanning, Zoned and layered blasting, Centre cutting effect, Caving filling