Abstract: In order to improve the top coal cavability of fully- mechanized top coal caving mining face in high ductibility seam,based on the experiment of physical and mechanical parameters of coal sample,from theoretical aspect,an analysis was conducted on the top coal difficult caving mechanism and weakening mechanism of fully- m echanized top coal caving mining face in high ductibility seam. UDEC simulation software was applied to numerical simulation on top coal caving condition at initial mining stage and the normal mining advancing stage of the coal mining face. The results showed that when the elastic modulus was lower than the roof strata,under the role of mi ne pressure,the deformation bending of the top coal would be higher than the roof and would cause the roof ditont well pass mine pressure to the top coal. Thus during the fully- mechanized top coal caving operation,the top coal would be difficult to be broken and fallen and a suspended roof would be easily formed. The top coal caving would be poor and would not be favorable to top coal recovery. After weakening measures conducted on top coal, during coal mining operation,the top coal falling condition was 0 bviously improved,the immediate roof would be caved with mining operation and would be well backilled in the goaf. The top coal cavability was good.