Four petroleum systems are studied in the Junggar Basin in this paper; they are the Carboniferous, Permian, Jurassic and Tertiary petroleum system. Among them, the Carboniferous and Jurassic systems are mainly gas-bearing systems, while the Permian and Tertiary are mainly oil-bearing systems. Based on the distribution of source rocks and the characteristics of oil and gas, the ranges of these petroleum systems are determined. The range of the Carboniferous gas-bearing system is a strip extending from Zhongguai-Shixi-Wucaiwan to the Santai Arch in the center of the basin; the Permian oil-bearing system includes the southern area of the northwestern edge and the Lunnan Arch; the Jurassic gas-bearing system is located in the southern part of the center uplift; the Tertiary system is limited near the Sikeshu sag in the southern margin of the basin. The formation and evolution of the four petroleum systems are also discussed in this paper, and the importance of critical moment in the formation of the petroleum system is emphasized.