Abstract：Based on the condition of No.6–1 coal seam of Suancigou Coal Mine，the caving characteristics of the top coal and roof，the bulk increase property and the stacking angle of the caved rock behind the powered support，the working resistances of the powered support and the coal face recovery etc. of the fully-mechanized sub-level caving full-seam mining with high bottom cutting height for the 20 m very thick and medium hard seam have been studied by 1∶30 physical simulation. Some conclusions can be drawn as follows. (1) It is feasible in technology to use full-seam mining for the 20 m very thick and medium hard seam by fully-mechanized sub-level caving mining with high bottom cutting height. (2) According to the top-coal caving and drawing characteristics，the mining process of working face may be divided into the initial mining stage，the transition stage and the top-coal normal caving stage in which the face coal recovery ratio n increases in a logarithmic form within certain distance of the face advance. (3) The coal face recovery may reach to 75% in the normal top-coal caving stage and the face coal recovery changes with the roof rock beam breaking periodically. (4) There are the phenomena of the full top coal cantilevering towards mined-area and then suddenly cutting down over the bottom working face wall. The front-rear stability of the powered support must be considered when designing and electing the support. (5) In order to ensure safety and top coal caving in time，the measures of pre-blasting or water pre-infusion to weaken top coal should be adopted.
