The invention provides an underground 
coal mine fracture sealing device and method. The underground 
coal mine fracture sealing device comprises a water injection 
pipe, a thick liquid return 
pipe, a front 
polyurethane hole sealing section, a back 
polyurethane hole sealing section, a 
safety valve, an umbrella type supporting device 
assembly and a thick 
liquid injection pipe. The umbrella type supporting device 
assembly is composed of an umbrella supporting frame, a supporting pipe, a sliding hoop, a 
piston rod and a 
piston, and a guide rail groove and the 
safety valve are arranged on the supporting pipe. When being fed into a 
drill hole, the umbrella type sealing device shrinks, and then the device is conveniently fed into the 
drill hole. When high-pressure water of which the initial 
injection pressure is 5MPa is injected, the umbrella type supporting device is opened, the 
piston is pushed forwards, the umbrella type supporting frame is unfolded and penetrates into 
coal, the high-pressure water continuously squeezes the hole sealing sections, and then the umbrella type supporting frame penetrates into the coal deeper and deeper. When the water 
injection pressure is increased to be larger than or equal to 15MPa, pressure water breaks through the 
safety valve to carry out fracturing operation on the 
drill hole, and therefore pressure loading capacity of the hole sealing sections is greatly improved, water 
injection pressure is increased, and the fracturing effect is improved. The underground coal mine fracture sealing device is simple in structure, easy to operate, high in pressure loading capacity, and good in sealing effect.