A method for drilling holes on a soft coal seam to measure coal seam gas pressure comprises the steps of drilling a shallow hole on the coal seam, placing an orifice pipe in the hole, utilizing cement slurry to fix the orifice pipe in the coal seam; performing drilling through the orifice pipe to the deep part of the coal seam, quitting a drill rod, injecting mixed slurry A and B to solidify coal around the drilled hole, performing drilling again along the originally drilled hole to exceed grouting depth by 3-5m; quitting the drill rod, inserting a capsule hole sealing device with a gas pipe and a water pipe in the drilled hole, sequentially connecting a push rod to push the capsule hole sealing device to be near the drilled hole grouting depth; on an orifice, respectively connecting the gas pipe and the water pipe with a connector on a flange cover, fixing the flange cover on the orifice pipe, utilizing a manual pump to inject water into the capsule hole sealing device in the drilled hole through a water pipe connector, and expanding the capsule hole sealing device to seal the drilled hole; injecting high-pressure cement slurry through a grouting valve on the flange cover, and connecting a gas pipe connector with a pressure meter, so that the gas pressure of the soft coal seam can be measured. The method is simple and convenient to operate, and a measurement device is simple.