Abstract: The upper part of the terminal slope of the northwest side of the open-pit mining pit of Jiaji‐ abao Iron Mine is the artificial crushed stone slope of the waste dump，the middle part is the thick soil slope of the quaternary，and the lower part is the composite rock soil slope of the fractured rock mass slope. Some sections of the original terminal slope angle are too steep，and some sections are too conservative. It is neces‐ sary to further optimize the composite slope angle to achieve the stability of the mine slope and the economic nature of mining. The research systematically sorted out the data on the geological and hydrological condi‐ tions of the slope，rock mass structure，etc.，and conducted a detailed analysis to identify the characteristics such as the rock mass structure and fault distribution of the stopes slope. It innovatively carried out the study of slope zoning，mainly using the limit equilibrium method for calculation and analysis and supplemented by the numerical simulation method. The results were compared and analyzed to calculate the slope stability pa‐ rameters of each zoning slope under different working conditions and comprehensively evaluate the stability coefficient of the composite slope. The results show that the hydraulic connection characteristics between the water seepage field in the slope rock mass and the surface water，as well as the dynamic changes with min‐ ing，the slope is generally in a stable state and has a certain amount of safety redundancy. The optimized slope angle increases from 40.3° to 43.3°，the outer boundary circle contracts inward by 18.6 m，and the dis‐ tance between the bottom toe line of the waste dump and the outer boundary circle increases by 18.6 m. This can reduce the amount of rock stripping by 115 000 m3 . This method can provide a reference for the engineer‐ ing research of composite slopes in similar open-pit mines.

Key words: open-pit mining, composite slope, slope stability, slope angle optimization