Abstract: In order to solve the problem of support instability at fully mechanized caving face in steep thick coal seam, the mechanical model of mutual influence among support, roof and floor is established. By analyzing the relation between every influential factor and support safety factor, the impact of working resistance and coal bed pitch is the most significant and the upper section of the face seems to be more unstable. Based on theoretical analysis, measures like pseudo-inclined caving, increasing support resistance are adopted, which acquires a favorable effect, guarantees the extraction safety of the face.