Abstract: In order to solve rib spalling problem of 8.5 m height fully mechanized face, main influence factors and characteristics of No.12401 working face in Shan gwan Coal Mine were studied through theoretical analysis, empirical regression analysis and numerical simulation methods.Plastic zone width formula was established based on D-P criteria modified by the Lord parameter. The rib spalling depth was determined by regression analysis based on mining height and plastic zone width. The results showed that in Shendong Mining Area, main influence factors of rib spalling were bearing pressure, mining height, periodic weighting and mining depth. The mai n failure form of No.12401 working face was shear failure type. For the working face, plastic zone width was 9.87 m, instable position was from 2.98 m to 3.59 m to roof, the rib spalling depth was from 2.85 m to 3.45 m.The comprehensive analysis through the modified calculation formula of the plastic zone width, theoretical analysis, re gression analysis can improve the reliability on the depth of coal wall spalling. These results can provide the basis for the design of the hydraulic support and selecting appropriate measures to prevent this phenomenon.