Abstract: Underground coal mining can adversely affect the stability of slopes in subsidence area.In this study，taking the instability failure of a slope in the subsidence area of Laohutai Mine in Fushun，Liaoning province as the example，the dynamic evolutionary process of instability of slopes in subsidence area is analyzed; Based on the three-zone theory，the rock masses in the east open pit slope located at the mining induced subsidence area are divided into four characteristic zones as caving zone，fractured zone，curve subsidence zone，and primary zone.Additionally，the coal mining depths corresponding to the three kinds of critical statuses are respectively calculated.

Key words: Subsidence area, Slope instability, “Three zones&rdquo, theory, Critical state