Abstract: In view of a series of safety issues such as roof breakage，inter-frame leakage，rib spalling and roof fall at the end of large mining height working face during weighting period，the No.85205 large mining height working face in Sandaogou Coal Mine is taken as the research object.Theoretical analysis，laboratory test and field measurements is used to obtain the strata behavior and key technology of rib spalling control in 5-2 coal seam of No.85205 large mining height working face.The results show that when the friction force between the coal seam and its overlying strata is equal to or greater than the uniform load，the interface between the coal seam and its overlying strata is prone to spalling，and when the friction force between the coal seam and its overlying strata is less than the uniformly distributed load，the coal seam at 0.578 times of mining height is prone to spalling.According to the analysis of the experimental data of coal strength，the coal wall of No.85205 mining face with large mining height is determined to be a Class Ⅲ unstable coal wall.According to on-site monitoring，the initial weighting step distance is 75 m，the periodic weighting step distance is 17.5～25.8 m，the average stepping distance is 22.7 m，and the influence range of lateral bearing pressure is about 14～16 m.The maximum top and bottom plates and the approach distance of the two sides of the section roadway are less than the warning value，and the support is finally combined with the comprehensive analysis of the working face，the "SIX-MUST" management technical measures for preventing rib spalling during equipment maintenance and comprehensive prevention measures such as increasing support force，laying protective net and dynamic omni-directional monitoring are put forward.