Based on the traditional David Jolley nine body stochastic simulation model, this article has designed a number of simulation programs of different drawing interval and refuse content. Research indicates that of top coal drawing body in this model upper width compared to lower width is small 1.3 ~ 1.7m, with the top coal drawing rate 50~71%. Improve the traditional stochastic simulation model of fully mechanized top-coal caving, considering temporary retention problems in top vacancy diffusion and horizontal fill issues in module. Under the same working face condition, it additionally builds the improvement simulation programs of different horizontal fill probability. Research shows that 10% increase in horizontal probability, the top coal drawing amount increases 2.2%. When horizontal fill probability reaches 30 to 40%, the top coal drawing ellipsoid body grows to be perfect.