The invention relates to a gas drainage method combining surface and underground fracturing and permeability improvement, and the method comprises the following steps: building underground large-
diameter directional long boreholes in a
coal reservoir or the top and bottom plates thereof under a
coal mine by using a drilling
machine; then building pressure relief holes in a
coal bed having an appropriate distance with the large-
diameter directional long boreholes; building vertical wells communicated with an underground large-
diameter directional long borehole filed or nearby roadways thereof from the ground to the underground; firmly connecting large ground fracturing equipment, a ground vertical well shaft and the underground large-diameter directional long boreholes by using
high pressure pipelines; carrying out fracturing on each underground large-diameter directional long borehole by using the large ground fracturing equipment to form a three-dimensional fracture network; discharging water in the underground large-diameter directional long boreholes and then carrying out continuous pressure extraction on fracturing holes and the pressure relief holes; and quickly extracting out the coal
bed gas through negative pressure by using the three-dimensional fracture network. According to the invention, the coal
bed gas can be extracted out quickly with high efficiency by using the three-dimensional fracture network and negative pressure, thereby providing a technical guarantee for safe and high-efficiency production of mines; and the method has the
advantage of wide application prospect.