Abstract: The rational span size of Zhangcunping mining is determined by the rock beam thoery analysis and the finite element calculation.Through the comparation of the compression strength between ore pillar and the C20 concrete artifical pillar，under the condition of 120m thick of cover rock，the size of C20 concrete artifical pillar greater than 5 m×5 m could make the safety factor of concrete pillar reach the number 1.0，which shows the replace of ore pillar by C20 concrete artifical pillar is feasible and could fulfill with the safety and stability during the recovery work of ore pillar，then can obtain the great economic benefit.

Key words: Phosphorite, Artifical pillar, Replacement, Finite element, Bearing capacity