Abstract: With weak surrounding rock，the ore body of an iron mine exists under the extra aeolian sand layer. Due to its small particle size and good liquidity，the caving method easily results in high dilution rate and loss rate. To ensure the safe and high-efficient mining of the lower ore-body，the project that keeps some horizontal barrier pillars under the contact surface of the Aeolian sand layer and ore body is put forward. The reasonable thickness of the horizontal barrier pillar is determined with the combination of the empirical formula and the numerical simulation FLAC3D. The results show that when extracting the 10 m span room without rib pillars by the open sublevel stoping method with subsequent backfilling and "taking one every the other one"，the setting-up 20 m barrier pillars are competent.

Key words: Extra aeolian sand layer, Barrier pillar, Safe thickness, Numerical simulation