Surface well-underground long borehole coal bed fracturing method

The invention relates to coal bed fracturing methods, in particular to a surface well-underground long borehole coal bed fracturing method. According to the method, a high-pressure pipeline is adopted to connect a fracturing unit on a ground well site with an underground long borehole, high-pressure fracturing liquid is injected into the high-pressure pipeline through the fracturing unit on the ground well site and enters a target coal bed under valve control, and the coal bed is cracked under the action of the high-pressure fracturing liquid, so that gas permeability is improved and methane of coal-mass comes out more quickly. According to the method, the advantages of surface high-pressure fracturing are utilized, the disadvantages of underground direct fracturing are avoided, a site where cracking rarely happens is selected, a fracturing pipeline is arranged in an underground roadway and connected with the ground fracturing unit for surface-underground combined fracturing, fracturing range is adjusted through the length of the fracturing pipeline and is wider than that of surface well fracturing, the ground fracturing site can be fully utilized, and pressure is higher and fracturing ranger is wider compared with underground fracturing.