NOVELTY - Holes are formed by drilling floor downward, to form gas inlet well and gas outlet well. A gasification passage is formed and gasification portion is divided into three working sections. Mining is carried out, ignition agent and gasification agent are added, the three working sections are heated, mixed gas is produced in oxidation zone and discharged to surface of wellhead, to obtain gas mixture of carbon monoxide, hydrogen and methane. The resultant product is subjected to combustion process in gas outlet portion and three working sections, to form slightly negative pressure.    USE - Production of coal gas (claimed).    ADVANTAGE - The method enables economical, environmentally-friendly and energy-saving production of coal gas with high recovery rate and gasification efficiency, by providing slight negative pressure to prevent diffusion of generated gases, escape of gases to the other direction and groundwater contamination.    DETAILED DESCRIPTION - Holes having diameter of 200-300 mm are formed by drilling floor downward in interval of 20-300 meters per floor distance, to form gas inlet well and gas outlet well. The hole is drilled to the lowermost portion of the coal seam, and gasification passage which is connected with gas inlet well and gas outlet well is formed integrally with gasification furnace which is located at the bottom of the coal seam gas well. The gasification portion of each channel between two well is divided into three working sections including oxidation zone, restore section and drying-pyrolysis section. Mining is carried out by air fracturing, and cross-sectional thickness of coal seam is made to less than 30 cm. Ignition agent is added to the oxidation zone between adjacent wells and gasification agent is added using gasification agent nozzles. The oxidation zone is heated at 900-1300 degrees C, restore section is heated at 550-900 degrees C and drying-pyrolysis section is heated at 200-550 degrees C. Mixed gas produced from the oxidation zone of the gas well is discharged to surface of wellhead, desulfurized, and impurities are removed to obtain gas mixture containing carbon monoxide, hydrogen and methane. The resultant product is subjected to combustion process in gas outlet portion and three working sections, to form coal gas.