Objective: The Penyijingxi Sag, one of the three hydrocarbonrich sags in the Western Depression of the Junggar Basin. has recently achieved significant breakthroughs in deep—ultra-deep natural gas exploration. However, research on the origin and genetic mechanisms of these deep—ultra-deep natural gas accumulations remains limited.Methods: This study systematically investigates the genetic types and source contributions of natural gas through comparative analysis of gas composition, carbon isotopes, and light hydrocarbon data with typical genetic end-members. Results: The results demonstrate that the genesis of deep—ultra-deep natural gas in the Penyijingxi Sag can be divided into three types: ① Typical humic type gas, mainly from the Carboniferous, characterized by deep burial, high maturity (dry gas) and localized distribution; ② Typical sapropelic type gas mainly derived from the Permian Fengcheng Formation source rocks, exhibiting widespread distribution, relatively low maturity (condensate oil and gas); ③ Mixed natural gas, which is mainly mixed from Permian Fengcheng Formation and Carboniferous source rocks. Then the proportion of mixed source gas was analyzed by Chemometrics. Based on these findings, a "dual-source hydrocarbon charging and paleo-uplift accumulation" accumulation model was established for deep—ultra-deep natural gas reservoirs in the Penyijingxi sag and its periphery.Conclusions: This research provides critical theoretical support for advancing hydrocarbon exploration in deep to ultra-deep strata of Western Depression.