The invention discloses a magnetic sealing device and method for a near-horizontal gas extraction drill hole of a coal seam. The magnetic sealing device for the drill hole comprises a first plugging bag arranged at a coal seam drill hole opening, a second plugging bag arranged in the coal seam drill hole, and an extraction tube, a grouting tube and a slurry return tube which are arranged in the coal seam drill hole, a space between the first plugging bag and the second plugging bag is a hole sealing section, magnetic grout is injected into the hole sealing section through the grouting tube, the grouting tube and the grout return tube both penetrate through the first plugging bag and extend into the hole sealing section, an installing rod is arranged in the extraction tube, and the end, extending into the extraction tube, of the installing rod is connected with a magnetic pole consistent with the magnetic grout in magnetism. The magnetic sealing device for the drill hole is simple in structure, reasonable in design, convenient to implement and low in cost, can be effectively applied to sealing of the near-horizontal gas extraction drill hole of the coal seam in combination with a drill hole magnetic sealing method, reduces energy loss, improves the hole sealing quality, and is good in hole sealing effect and convenient to popularize and use.