There is a particular characteristic in the for-mation of the Upper Paleozoic gas pool in the Ordos Basin that is its water-gas interface migrated regional during geological history.However,there has been lack of detailed research on this paper,the formation time of hte fluid inclusions formed in the water-gas transition zone of the gas pool was deduced using their trapping temperatures and combining of the burial with geothermal history of the basin.On the basis of this,the isochrone of water-gas interface migration for the gas pool was mapped .The result shows that the gas pool began to form around the yanan Area at about 165Ma,and then developed and enlarged toward the north direction.The gas pool finally formed at about 129 Ma.Since the basin uplifted from the late Cretaceous and gas supply decreased,the water-gas interface of the gas pool migratec back to the present position.