Abstract: In view of the difficulty of fully-mechanized mining in steeply inclined coal seam with thickness of 4 to 8 m，the horizontal sublevel short wall fully-mechanized caving method was proposed innovatively. In the No. 3-3c steeply inclined coal seam of Longquan Coal Mine，the single roadway integrated with excavation and recovery was arranged as working face，the pillar on sides of roadway was recovered ahead by spiral drilling machine，and the top coal was recovered by the vertical and horizontal self-moving supports. The Z-type ventilation was formed by constructing a ventilation roadway along the side of gob. Through theoretical analysis，numerical calculation and physical similarity simulation，the main mining parameters，including sectional height and ratio of mining height to caving height，were determined，and the characteristics of roof movement evolution，floor failure and sliding and the generalization of surrounding rock bearing structure were revealed. The results show that the effect of coal caving is better when the section height is 10 m and the ratio of mining height to caving height is 2.85. The cross-layer inclined masonry structure with multistage ladders is formed by migration of the critical layer，and the failure and slip modes of floor are extruding-translation，extruding-underdraught and extruding-upthrust in different areas of horizontal sublevel caving stope. Roof，pillar and floor are interrelated to form the roof-pillar-floor(R-P-F) chain structure. When the height of section with three sublevels is 30 to 45 m，the mutual conversion of strong and weak chains between structural units can be cut effectively in mining process，and the impact disaster caused by the roof falling over great extent and the instability of pillar can be prevented. The new mining method proposed and studied above provides the technological and theoretical basis for the safe and efficient production of such coal seams，and is of great significance to the sustainable development of coal in Xinjiang Region and even western China.