Abstract: In order to study the law of the mining and caving ratio affected to the top coal recovery rate of ultra tick seam in a mine of Zhungeer coalfield, a PFC2D numerical analysis program was applied to a simulation study on the top coal cavity of the different mining and caving ratio and the different top coal caving step distan ce.The paper analyzed the relationship between the mining and caving ratio and the top coal recovery rate under the certain thickness of the seam and analyzed the dif ferent top coal caving step distance affected to the top coal recovery rate under the same mining and caving condition.The study results showed that when the mining a nd caving ratio was over 0.35, the top coal would have sufficient loose space and could be successfully caved .According to the mining technical condition, when the mi ning and caving ratio was 0.48 and the top coal caving step distance was 1.6 m, the top coal caving effect would be the best.