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The resistance transfer coefficient of supports plays an important role in support selection in coal mines, which is the main factor in support crushing accidents. Based on the key layer theory, the formula for calculating the resistance transfer coefficient of supports under the load of a loose layer was deduced. The analysis of four working faces with thick loose layers and the corresponding mining pressure data were used to deduce the load transfer coefficients of the thick loose layers and ultimately illustrate the relationship between thick loose layers and different influencing factors. By using microseismic technology to monitor the process of roof failure in a thin bedrock working face with a thick loose layer during mining, the roof failure characteristics of a large-mining-height working face under the load of a thick loose layer were further verified. The results show that a thicker loose layer and thinner bedrock caused more of the load to transfer to the working face, the roof microseismic events were mainly concentrated in the range of 60 m to 75 m above the coal seam, and the most active events occurred during the square stage (the length of the working face’s goaf is equal to its width). The height of the water-conducting fracture zone was analyzed by microseismic data and then verified with theoretical calculations.