Abstract: Aiming at the core problem of top coal cavability at full-mechanized caving face with large mining height in close coal seams, the damage mechanic properties of mined and un-mined at upper coal seam were analyzed through theoretical analysis, the distribution of abutment pressure and the fractures development and the breakage of top coal were simulated by numerical model. The result shows that the top coal cavability which was indicated by the damage degree of top coal was affected by the original fissures and abutment, compared with the un-mined upper coal, the mining of the upper seam increased the original fissures of lower seam, and increased the abutment pressure of lower coal seam, and then increased the cavability of the top coal.