Abstract: Aiming at the engineering problems of high boulder rate and serious damage of stope eye⁃ brow line in deep hole blasting in sublevel caving method without sill pillar of No Ⅱ ore body in Tongshan Mine，in order to improve the shoveling efficiency and ensure the safety of underground mining operation， based on the superposition theory of reflective tensile stress wave，combined with the physical and mechani⁃ cal characteristics of ore body and rock，similar mine engineering experience and extrusion blasting empiri⁃ cal formula，the key technical parameters of medium and deep hole extrusion blasting are systematically op⁃ timized and determined. The minimum resistance line (row spacing) of reasonable blasting is determined to be 2 m，the hole bottom distance is 2~2.5 m，the hole mouth distance is 0.8~1.4 m，the unit explosive con⁃ sumption is 0.4~0.45 kg/t，the caving step distance under conventional working conditions is 4 m，the caving step distance under local strengthening blasting conditions is not more than 5.1 m，and the millisecond inter⁃ val between rows is 50 ms. The optimization design of charge structure is completed. The industrial test veri⁃ fication was carried out based on four mining routes in 330 m section of the mining area.The results show that after the implementation of the optimization scheme，the lump rate of ≥ 700 mm ore rock is reduced to less than 5%，the damage times of the eyebrow line of a single route are no more than 2 times，the consumption of secondary crushing explosives is less than 0.15 kg/t，and the ore output of the scraper is increased to more than 1 200 t. Reasonable matching of row spacing and hole bottom spacing，and accurate row-to-row milli⁃second timing can achieve efficient superposition of blasting stress waves. With the optimized orifice protec⁃ tion charge structure，it is the core key to control the blasting block rate，suppress the eyebrow line damage， and achieve safe and efficient mining in mines.The research results can provide reference for the optimization of deep hole extrusion blasting parameters in the non-pillar sublevel caving method of similar hard deposits.

Key words: sublevel caving method without sill pillar, medium-deep hole extrusion blasting, caving step distance, millisecond delay time