Abstract: Mahu Sag, located in the Junggar Basin, is a significant oil and gas-rich sags primarily distributed in the Permian, Triassic, and Jurassic, exhibiting complex oil and gas properties. In this study, source rock samples of Fengcheng Formation (P₁f), Xiazijie Formation (P₂x), Lower Wuerhe Formation (P₂w), and Karamay Formation (T₂k) in Mahu Sag and the crude oil samples of Baikouquan Formation (T₁b) in Aihu oilfield were used as the main research objects. Various analytival techniques, including TOC analysis, rock pyrolysis, carbon isotope, saturated hydrocarbon chromatography, saturated hydrocarbon chromatography-mass spectrometry, and single well burial history-thermal history analysis, were employed to clarify the crude oil source in Baikouquan of Mahu Sag. The results demonstrate that the organic matter abundance of Fengcheng Formation in Mahu Sag surpassed that of the source rock of Lower Wuerhe Formation, with abundant organic matter content. The organic matter in the studied formations is primarily identified as type II kerogen, indicating a high oil generation potential. The crude oil extracted from the Baikouquan Formation has reached maturity, and its origin can be attributed to the prevailing weak oxidation-weak reduction sedimentary environment. Through oil-source correlation, the crude oil biomarkers in Mahu Sag and Fengcheng Formation source rocks were found to be well comparable, underscoring the significant contribution of Fengcheng Formation source rocks to the crude oil in the area. Two distinct stages of crude oil filling were identified in the Baikouquan Formation reservoir. The first occurred during the Early Jurassic, while the second took place in the Early Cretaceous periods. Both stages are closely associated with hydrocarbon generation and expulsion within the Fengcheng Formation source rocks.