Abstract: In order to measure the effective gas drainage radius of mining-coal bed accurately, the arrangement of drilling holes in the traditional pressure dropped measurement are improved appropriately and a new borehole layout method which is named "the drainage and the pressure measurement" is proposed. In the same height, unequal spacing of drainage holes and pressure measurement boreholes are arranged separately, the gas effective extraction radius is determined by monitoring the gas pressure changes in the pressure measurement borehole and the pressure drop curve. The field test result shows that the gas effective drainage radius is increased as pre-drainage time prolonged, the effective drainage radius is 1.5 meters after 12 days gas extraction, and then it reaches to 2 meters after 20 days gas extraction, after 60 days gas extraction, the gas effective drainage radius is 3.5 meters, and it approaches 4 meters, since then the influence scope of gas drainage expands no longer.