The invention discloses a permeability-improving extraction system of a coal seam in a borehole. The system comprises a hydraulic flushing device, a pre-split blasting device, a gas extraction deviceand a safety monitoring system which are all arranged in a coal mine underground extraction roadway, a coal seam bottom plate, a coal reservoir and a coal seam top plate are arranged at the top of theextraction roadway sequentially from bottom to top, the hydraulic flushing device comprises a boring machine, a drill stem, a drill bit, a high-pressure water injection pump and a water gas separator, the pre-split blasting device comprises a detonator, a lead and a PVC tube, the gas extraction device comprises a branched extraction pipe, a main extraction pipe and gas extraction equipment, and the safety monitoring system comprises a detection module, a processing module, a collection module, an on-off input-output module and a pipeline valve arranged on the branched extraction pipe. By thesystem, safety of gas extraction control is improved, gas accidents can be prevented effectively, coal seam permeability is improved effectively, gas extraction effect is improved, extraction time isreduced effectively, and gas potential safety hazards are lowered to greatest extent.