Inherited regional marine sediments developed in Ordos region from middle-late Proterozoic to early Paleozoic erathems, during which three major evolution stages went through, including middle-late Proterozoic continental rifts and aulacogens, Cambrian epicontinental platform and Ordovician restricted platform and tectonic conversion. It is deemed that there was a sedimentary facies belt favorable for gas accumulation along the margin of troughs/platform in the western and southern parts of Ordos Basin. The Middle-Upper Ordovician Pingliang and Beiguo Formations are the main source rock beds for the Lower Paleozoic gas accumulation in the western and southern parts of Ordos Basin. Ordovician reef/shoal lithologic traps are common reservoirs and two areas, the northern Tianhuan area in the western part of basin and the northern Youling area, are the recent object ones favorable for gas exploration.