Karst developed well in coal measures strata in the Chongqing area, and some karst contains a large amount of poisonous gas. When karst is uncovered, poisonous gas may be to exhale or outburst. The main component of the poisonous gas is methane. The Songzao mining area hosts the most karst in the Chongqing region, while the Shihao coal mine and Datong No.1 mine are the most serious karst in the Songzao mining area. The coal-bearing strata in this mining area are Longtan formation of upper Permian. The thickness of coal measures strata is 66 meters to 80 meters, with 10-12 layers of coal-bearing strata. The total thickness of coal is 4.01 meters to 9.88 m, 7.58 m on average. Among them, M6, M7 and M11 coal seams in local mineable seams have outburst danger, while the M8 coal seam in the whole area is a serious outburst coal seam.The problem of karst gas has become an important disaster-causing factor affecting and restricting the safety of coal mine production. In order to ensure the construction safety of rock roadways in karst-affected areas and effectively prevent and control the karst gas disaster, the source and the occurrence law of karst gas in the Songzao mining area are analyzed by means of theoretical analysis and site tests. Results show that the main source of karst gas is the coal measures strata located at the top of Maokou limestone, i.e. M12, M11, M10, M9, M8, M7, and M6 coal seams in the mining area. The broom structure, semi-filling karst cave and concealed structure are gas enrichment areas, and low permeability of overburden rock in coal measures strata is also a key factor for generation of karst gas. The 12# gas roadway in the north three mining area of the Shihao coal mine and the W1603E gas roadway in the west No.1 mining area of Datong No.1 coal mine are selected as the test roadways. The "four-in-one" prevention and control technology of karst gas is adopted, which includes，(1) Prediction of small karst gas blocks; (2) Step-by-step local detection measures consisting of geophysical exploration, drilling and drill rod detection; (3) Local karst gas prevention and control technology with winding, draining, ventilating and plugging; (4) Safety protection measures. On-site application shows that strict implementation of "four in one" prevention and control technology can effectively prevent karst gas accidents, and can effectively use karst gas to ensure safe and orderly roadway excavation.