Abstract：It is key problem to raise the top coal recovery rate of the fully mechanized sublevel caving mining. Weakening top coal by using water pre-infusion is one effective method to solve this problem. The mechanism of permeation movement in cracks and porosity of water infused into the coal mass ahead of the working face and the weakening of the coal mass is theoretically studied. By laboratory test，the law of weakening of the coal mass deformation modulus from the water pressure are obtained and the law of weakening of the coal mass compression strength from the water-bearing ratio are obtained. The method to determine the water infusion engineering parameters，such as relative position of water infusion to the working face，the start and stop times of infusion，water-bearing ratio of water infusion，infusion volume，wetting radius，interval of infusion holes，infusion duration，infusion pressure and the hole layout，is proposed. The remarkable technical and economical effects and social benefit have been achieved by application of the study results to the working face 4309 of fully mechanized sublevel caving mining in Lu¢an Wangzhuang Mine.
