Abstract: Several characters of CO₂ deposits can be used to judge the origin of CO₂, such as the percent of CO₂, the percent of companion hydrocarbon, the percent of inert gases and their isotopes, geology background of CO₂ generation, δ¹³C_CO2 and carbon isotopes of companion methane homologous series. The percent of CO₂ in Changdedong gas deposit is 89%~90%, δ¹³C_CO2 is-4.06 ‰~-6.61 ‰, which is belong to the area of inorganic origin, ³He/⁴He is 3.9 ×10^-6 and 4.5 ×10^-6, which is between the mantle origin and crust origin. Carbon isotopes of companion methane homologous series reverse order, which have the character of inorganic origin. The judgement of more detail origin of this CO₂ deposit is dependent on the researching of deep geology structure of northern Songliao basin and exploring new geochemical criterions such as CO₂/³He, etc.