Abstract: A series of large and low?abundance lithologic gas fields developed in the Permian of Ordos basin are significant domains for natural gas exploration nowadays. The formation mechanism of Yulin gas field has revealed that under the large flat structural setting,fluvial?delta sands and source rocks are widely distributed and mutually contacted as a“sandwich?type”, providing geologic conditions for large?scale gas accumulation in this area; regional tectonic uplift and denudation as well as large?sized thin sand reservoirs are the primary causes for forming low abundance in Yulin gas field; the distribution of“dessert”of such a field is controlled mainly by quality of transport system, particularly in areas with thick belt sand body and fracture transport systems in which gas concentration is normally high. Based on the geochemical data of fluid inclusion and gas component, combined with structural and depositional evolutions, the formation of Yulin gas field is divided into three stages：preliminary hydrocarbon emplacing and reservoir quality transforming stage in Early?Middle Jurassic; lithologic gas pool forming stage by optimized allocation of gas accumulation factors in Early Cretaceous; Late Cretaceous to nowadays,effective coupling of tectonic uplift and large?sized thin sand reservoir makes the surviving field become large gas field with low abundance until now since Late Cretaceous