Abstract: In view of the actual mining engineering of two-step filling mining method in an iron mine， the numerical simulation tool of LS-DYNA is used to explore the regulation mechanism of the size of the pil⁃ lar on the stability of the filling body. During the mining period，the filling body needs to bear the coupling effect of the static load of the overlying surrounding rock and the dynamic load of the two-step mining blast⁃ ing. The reasonable setting of the thickness of the wall protection pillar is the key projects to weaken the blasting disturbance and ensure the stability of the filling body. The thickness range of 1.2 ~ 2.3 m typical wall protection pillar is selected，and the Von Mises stress evolution and displacement response law of fill⁃ ing body under different sizes are systematically analyzed. The numerical calculation results show that when the thickness of the pillar increases，the maximum stress of the filling body shows a significant decreasing trend. The peak stress at the thickness of 1.2 m reaches 2.20 MPa，and the thickness of 2.3 m decreases to 0.80 MPa，a decrease of 63.77 %. When the thickness is greater than 1.5 m，the stress distribution of the filling body tends to be stable，which can effectively avoid irreversible damage. The displacement of filling body under different retaining wall thickness is much lower than the damage threshold. According to the re⁃ quirements of safe mining and resource utilization efficiency of comprehensive mining engineering，it is sug⁃ gested that the thickness of wall protection pillar should not be less than 1.5 m. This study provides a theoret⁃ ical basis for the optimization of engineering parameters of retaining pillars in filling mining method，and has important practical value for improving the safety of iron ore mining and reducing engineering risks.