There contains non-hydrocarbon CO₂ and N₂ universally in natural gas of Y basin and the N2 content appear negative-correlate with overall of inorganic CO₂ and positive-correlate with hydrocarbon gas which mainly is CH₄. According to N₂ content .natural gas can be divided into three typesjow N₂ content(N₂<10%) .middle N₂ content(N₂ = 10%-15%),high N₂ content(N2>15%). According to its geology and geochemistry behaviors and characteristics of companion rare gas isotope the origin of N₂ can be comprehensively discriminated and determined to three original types:atmospheric origin,shell origin and combination of shell origin of hydrocarbon and non-hydrocarbon. The distribution traits largely possess parti-tioned-area and partitioned-block on plate and concentrated in shallow layer or overshallow of 400-1600m on cross section. The co-existed grouping relation of N₂,CO₂ and hydrocarbon gas usually include natural gas of high-content N₂association with low-content CO₂ hydrocarbon gas of hydrocarbon origin and hydrocarbon gas of mainly high-content CH₄,and N₂nuaural gas of hydrocarbon and non-hydrocarbon combination origin coexisting with high-content CO₂ of non-hydrocarbon and partly hydrocarbon gas which mainly is CH₄. Obviously this co-existed grouping relation determine the traits of origin and composition of N₂. So based on the origin type of N₂ and co-existed grouping relation and distribution characteristics of N₂, CO₂ and hydrocarbon gas, associated with integrated analyzing and researching of geology and geochemistry, the source of N₂ can be comprehensive discriminated and determined.