Existing researches on the evaluation of pressure relief effects are mostly aimed at inclined or gently inclined coal seams. The applicability to near-vertical extra-thick coal seams is not yet known. It is difficult to judge the pressure-relief effect of near-vertical extra-thick coal seams after pressure-relief blasting. Taking the B3+6 coal seam in the southern mining area of Wudong Coal Mine as the engineering background, combined with on-site monitoring and theoretical analysis, the decompression effect of the near-upright extra-thick coal seam is studied by using the mine transient electromagnetic. The study found that the apparent resistivity of the coal seam and its roof and floor coal in the pressure relief area after the implementation of deep and shallow hole pressure relief blasting and coal seam water injection is significantly reduced compared with the unrelief area, and the apparent resistivity of the roof is reduced by 50%~58.33. %, the coal seam is reduced by 28.57-42.86%, and the floor is reduced by 70-80%. It shows that the degree of fracture development in coal and rock masses increases, the load-bearing capacity of surrounding rocks decreases, stress concentration is not easy to occur, and the pressure relief effect is good.