Abstract: This paper divides Meso-Cenozoic in Caidam basin into three petroleum systems of Jurassic, Tertiary and Quaternary, among which Jurassic system is oil and gas half system, Tertiary is one dominated by oil, and Quaternary is one by gas. The formation and evolution of these three petroleum systems are analyzed. Based on the distribution of source rocks and generated oil and gas, the ranges of each system distribution are classified: Jurassic petroleum system is in northern Caidam basin, with E-W stretching band dominated by fault block zone in its northern margin toward Jianshan, Yahu and Yanhu areas in south; Tertiary petroleum system is mainly along Mangya depression in western Caidam basin, stretching along Yiligou, Hongsanhan No.4, boat like dome and Huangshi Structures; while Quaternary gas-bearing system is distributed in Sanhu depression of center-eastern Caidam basin.

Key words: Caidam basin, Jurassic, Tertiary, Quaternary, petroleum system, formation, evolution, distribution