The invention discloses a hole sealing method of a coal mine underground hydraulic fracturing hole, which carries out the hole sealing by using a double-capsule hole sealing device. The method comprises the following steps: (a) drilling a fracturing hole to a set depth by using a drilling machine in an extraction roadway and recording the thickness of a corresponding rock layer according to the characteristics of the rock layers distributed in depth direction of the fracturing hole; (b) determining the length of a medium connecting pipe between a first capsule and a second capsule of the double-capsule hole sealing device according to the thickness of the rock layers with various characteristics of the fracturing hole and preparing the medium connecting pipe; (c) assembling the double-capsule hole sealing device and placing the double-capsule hole sealing device into the fracturing hole, so that the first capsule is placed in a bottom plate layer of coal layers, and a front end of the first capsule is located at the intersection of the bottom plate of coal layers and the coal layers; and (d) connecting a fracturing pipeline and starting a fracturing pump unit, and pouring the water into the coal layer for fracturing so that the first capsule and the second capsule respectively form sealing with the corresponding sections of the fracturing hole walls. The coal mine underground hydraulic fracturing hole sealing method has the following beneficial effects: no potential safety hazard caused by fracturing liquid leakage occurs when the fracturing is carried out, and the hole sealing efficiency is high, the hole sealing effect is good, the practical range and the pressure resistance are wide, and the method can realize repeated utilization.