Abstract: This paper is aimed atresearching on the Tertiary CO₂ gas pool-forming conditions in Shangdu basin,by means of analyses for regional structures(fractures,volcanicities, magmatism),stratig raphic cha racteristic and sedimentary facies as well as results of the sesmic exploration,Carboniso tope of CO₂ and helium isotope;and conditions of the source, migratory path way,reservoir,trap,capping bed of CO₂ gas and forming model of CO₂ gas reservoir have been d iscu ssed in the paper.It is considered that CO₂ gas in this area,passing through the Wulanhada-Gaowusu deep fault in to Tertiary reservo ir bed,com es from the mantle and then has been enriched.The coarse clastic rock in Tertiary river deposits(or alluvial fan)is sowidesp read,thick and lower in diagenesis degree that it has favorable condition for reservoir;and the late Neogenelacu strine deposits are turned in to very thick mud stone capping beds.The postdepo sitional compacting,fracting,volcanism and magmatism and soforth caused local structures in the area well-developed and formed some lithostructural or structural-litho traps,which are favorable for CO₂ gas reservoir forming.