The natural gases found in the Yinggehai basin have nitrogen gas content ranging from 3.5% to 35%, and carbon dioxide content ranging from 0.1% to 93%. The nitrogen and CO2 con-tents show a wide variation even in the same gas field. The natural gas generation and evolution model has been established based on the relationship among the contents of nitrogen, carbon dioxide and hydrocarbon gases in the discovered gas fields, and the results of simulation experi-ments. The thickness of the Tertiary and Quaternary in the Yinggehai basin is over 17 km, and gas generation stages from diagenesis (microbial methane) to metamorphism have been developed. Nitrogen in this basin is organic in origin, and has been generated mainly in the catagenetic stage, roughly synchronous with hydrocarbon gases. Carbon dioxide is mainly inorganic in origin, and has been generated from high-temperature decomposition of carbonates in the metamorphic stage. The Dongfang gas field shows strong inter-reservoir compositional heterogeneities, and different gas reservoirs have recorded the products of gas generation at different stages. It has been con-firmed that the complexity in natural gas composition in the Yinggehai basin is the combined re-sults of multi-stage natural gas generation and multi-stage gas injection and accumulation. The natural gases found in the Yinggehai basin have a nitrogen gas content ranging from 3.5% to 35%, and carbon dioxide content ranging from 0.1% to 93%. The nitrogen and CO2 con-tents show a wide variation even in the same gas field. The natural gas generation and evolution model has been established based on the relationship among the contents of nitrogen, carbon dioxide and hydrocarbon gases in the discovered gas fields, and the results of simulation experi-ments. The thickness of the Tertiary and Quaternary in the Yinggehai Basin is over 17 km, and gas generation stages from diagenesis (microbial methane) to metamorphism have been developed. Nitrogen in this basin is organic in origin, and has been generated mainly in the catagenetic stage, roughly synchronous with hydrocarbon gases. Carbon dioxide is mainly inorganic in origin, and has been generated from high-temperature decomposition of carbonates in the metamorphic stage. The Dongfang gas field shows strong inter-reservoir compos it has been con-firmed that the complexity in natural gas composition in the Yinggehai basin is the combined re-sults of multi-stage natural gas generation and multi -stage gas injection and accumulation.