Abstract: By comprehensive analysis on the petroleum charging conditions,migration and entrapment patterns,and space distribution rules of the Mesozoic petroleum systems in Northwest China,they are classified by geneses into 24 petroleum systems. Based on system types,hydrocarbon resource amount,trap styles,target stratum depth,petroleum accumulation and shows as well as the other factors,the petroleum systems are evaluated preliminarily. It is suggested that the Jurassic petroleum system in the southwest of the Tarim Basin,the composite petroleum system in the guasi southeast of China and the Jurassic petroleum system in the northern edge of the Qaidam Basin should be taken as emphases for the strategic area-selection of petroleum exploration.