The invention discloses a method for testing pressure of gas in a water-containing wall rock coal seam. The method comprises the steps of: (1) selecting a pressure testing place in a rock layer tunnel; (2) estimating the thickness of the coal seam at the pressure test place; (3) selecting thickness of a water plugging coal pillar, wherein the water plugging coal pillar is a part between a hole bottom after the hole is drilled in the coal seam and a water-containing layer, and the thickness of the water plugging coal pillar is a vertical distance between the bottom of the drilled hole and the water-containing wall rock; (4) designing the drilling direction and the position of the hole, and computing the length of the coal hole according to an included angle between the drilling direction of the hole and the trend of the coal seam, the thickness of the coal seam and the thickness of the water plugging coal pillar; (5) performing drilling at the pressure testing place, and stopping drilling until the drilling construction enters the coal seam and reaches the designed coal hole length, thereby completing the drilling construction; and (6) sealing the hole and testing the pressure. By utilizing the basic characteristic that the coal seam is an impermeable stratum, the invention provides a method for testing the pressure of the gas in the water-containing wall rock coal seam, which can directly eliminate the influence of the water-containing wall rock (roof or bottom plate) when the hole is formed.