Abstract: Well Y intersects several natural gas strata in Hari depression, Yingen-Ejin basin. It is characterized by open flow capacity of 91500m³ natural gas per day after hydra perforating and fracturing between 2946.5m and 2951.0m. This paper has no suspect on the oil source of the superficial zone of this well, which came from the Cretaceous Yin'gen Formation. Additionally, there exists controversy on the stratigraphic age of the industrial gas flow. Based on the Roversus depth correlation and geochemical characteristics discrimination of well mudstones, the unconformity between the Permian and the Cretaceous Bayin'gebi Formation was identified in the depth between 2593.80m and 2909.60m. Meanwhile, the gamma ray and specific resistance curve of the geophysical log revealed obvious changes at the 2792.0m of the tenth coring. Moreover, this research confirms that 2792.0m is the unconformity between the Permian and Cretaceous Bayin'gebi Formation. Particularly, it means that the natural gas derived from Permian has good hydrocarbon prospects. The oil-gas exploration in future should mainly focus on the Permian strata.