Abstract: In this paper, discrete element method is used to obtain macro and micro mechanical parameters of coal from experiment and numerical simulation. Hard top-coal caving mining model is established to analyze coal falling process and dropping shape before and after weakening. The research results show that macro and micro mechanical parameters are reduced greatly after weakening hard top-coal, and after water injection and blasting in hard top-coal, the bonding force of coal particles is only 63% and 55% of that before weakening. Water injection or blasting in hard top-coal weakens significantly the tension among the coal particles, and the released amount of top coal after weakening is much larger than that before weakening. After water injection weakening top coal, the top coal recovery rate reaches 82.6%, and after blasting weakening top coal, the top coal recovery rate reaches 89.43%, while the top coal recovery rate is only 54.47% without weakening measures.