The invention discloses a composite fracturing and uniform permeability-improving method for tree-like boreholes in coal seams of an underground coal mine. The composite fracturing and uniform permeability-improving method is suitable for permeability improvement of soft low-permeability coal seams, and is characterized in that a gas exhausting and mining hole serve as a mother hole, uniformly distributed self-advancing boreholes serve as tree-like son boreholes, and a tree-like borehole net is subjected to hole-sealing fracturing. Compared with a conventional hydraulic fracturing method, the composite fracturing and uniform permeability-improving method can realize uniform fracturing of the low-permeability coal seams to enlarge the fracturing range of single crossing boreholes, so that uniform permeability improvement is achieved, and the shortcomings that the crossing boreholes subjected to conventional hydraulic fracturing are low in utilization ratio, and a single major fracture can damage top and bottom beds are overcome. The composite fracturing and uniform permeability-improving method is simple to operate, large in permeability improvement range and good in permeability improvement effect and provides a guarantee for safety production of the underground coal mine.