Abstract: The slope of open-pit mine is mainly rock slope，and its common failure form is the plane failure or wedge failure of slope steps. Taking a gold mine in Inner Mongolia as the research object，based on the on-site fine investigation of the rock mass structural plane，the stability and failure mode of the slope steps of the open-pit mine are studied qualitatively and quantitatively. According to the research re⁃ sults，the step parameters of each lithologic slope are recommended: the step slope angle of chlorite quartz schist is 51°~53°，which should not be merged，and the step height is 9 m. The step slope angle of quartz⁃ ite，rhyolite porphyry and sericite quartz schist is 65°~70°，and can be merged，the step height is 9 m， and the back step height is 18 m.

Key words: open-pit slope, step destruction, structural plane, stereographic projection