The invention discloses a method for determining the effective influence radius of a high-pressure medium injection drilled hole of a coal seam. The method includes the steps of coal seam drilling, coal seam sampling, preparing of saturated electrolyte, injecting of the saturated electrolyte, salinity comparing, determining of the final effective influence radius of the injection drilled hole andthe like. According to the method, on-site collected water samples or coal samples in a coal seam are adopted to measure the original salinity in the coal seam, after the saturated electrolyte is injected into the high-pressure water injection drilled hole, the salinity after injecting of the saturated electrolyte is measured to be compared with the original salinity of the coal seam to conduct curve fitting so as to measure the effective influence radius of the high-pressure medium injection drilled hole of the coal seam, the influence of geological factors such as original water in the coalseam on test results can be reduced to the maximum limit, meanwhile, the most accurate test results can be quickly obtained with the minimum engineering amount and the minimum time loss, and thus thetheoretical basis and data support are provided for reasonable arrangement of the high-pressure medium injection drilled hole.