Abstract: The predominant rock-mass structural planes control the boundaries of rocky slope deformation ，and their combination decides the type of deformation and failure.For a coal mine，the rock-mass structures of rocky excavated slopes in mining engineering were investigated and studied.The predominant structural planes were grouped，and the mining slopes were divided geometrically and lithologically into several sections.The associations of predominant structural planes with the inclining direction/angle of step excavation slopes were intuitively analyzed on Dips.Based on this，the occurring conditions for the failure type due to mining step excavated slope are discussed.The targeted engineering treatment measures should be applied after excavation of mining step slopes.The step slopes in danger areas can be sectionally treated by analyzing the possible areas and positions of structural planes′ stereographic projection.Thereby，safety production and cost saving in mines can be both guaranteed.

Key words: Structural surface, Rock slope, Failure type, Mining engineering, Sectional