Abstract: Based on hydrocarbon formation in modern volcanic activities and Simulation experiments of hydrogenation, sedimentary environmewts and hydrocarbon-generation characteristics of source rocks associated with volcanics in faulted basins were studied and summarized,and the concept of semi-inorganic gases was suggested. The enviroment of volcanic spout and effusion is presupposition essential for low mature sowrce rocks to produce hydrocovrbons effectively;and hydrogenation of magmatic hyperthermal gas-liquid upon sedimentary organic matters is thecondition for the generation of semi-inorganic gases. Due to different modes of volcanic Eruption-effusion. different types of semi-inorganic gases were generated.