Abstract: Hydraulic fracturing is an important technology for increasing permeability and productivity in the process of CBM development. The influence range of fracturing is directly related to the design and optimization of hydraulic fracturing scheme. As one of the key technologies, monitoring the sweep range of underground hydraulic fracturing in coal seam is a difficult technical problem to be solved urgently. In order to obtain the influence range of underground hydraulic fracturing in coal seam, according to the physical characteristics of coal seam and surrounding rock during fracturing, microseismic monitoring of fracturing influence range of three boreholes in a coal mine was carried out by using underground microseismic monitoring technology. The traditional borehole observation method was used to verify the monitoring results. The results show that the underground microseismic monitoring technology can obtain the fracturing damage range, but the fracturing damage range delineated by microseismic monitoring is smaller than that by borehole observation method. It is due to the soft coal seam and the large attenuation of seismic wave. The fractured surrounding rock or coal seam is seriously fractured, which is not conducive to the generation and expansion of fractures. So there fewer microseismic events are received.