Abstract: The shallow gas in the south of Songliao basin mainly existes in late Cretaceous strata. According to component analysis, it is methane type biogas . Organic geochemical shows that the biogas source bed has strong or relatively strong reducing environment and rich, good- typed organic matter. The continuance sedimentation, speedy sediment and good sedimentary environment are the important geology factors to forming shallow gas. Favorable reservoir and seal conditions are conductive to its congregation and conservation. The favorable reservoir rock layer in this area is mainly built up by fine sandstone, and it has the character of shallow concealed, new era, loose and unconcretion. The deposition time from Quantou Formation to Nenjiang Formation in the Cretaceous strata is the heyday of large-scale depos-its hollowly's formation and development. In the depression term, lake areas and deposit centers form in the centre of thebasin. The lake area is more than 80 thousand square kilometers, where deposits the most favorable hydrocarbon layer of Songliao basin and as well as a good regional cap rock.