Abstract: The Turpan-Hami Basin is the only one discovered in China whose hydrocarbon is dominated by coal related oil. The Taibei Sag is the major one of the basin, and is also the one in which the most amount of hydrocarbon is discovered. Having the hill tectonic zone as the boundary, the Taibei Sag can be divided into the west and the east two parts. The eastern crude oil has the typical characteristics of coal-related oil, and the characteristics of the western crude oil are between lake facies oil and coal related oil. To look at the surface, the western crude oil possesses the characteristics of mixed sources; but the analysis on the carbon isotope, the ratio of saturated and aromatic hydrocarbons and the ratio of pristane and phytane for crude oil shows that the distributive ranges of these indexes for the western crude oil are obviously small than those for the eastern crude oil. Therefore, the western crude oil cannot consist of lake facies oil mixed with coal-related oil; it may be formed in the Middle-Lower Jurassic lake facies mudstone whose features are between typical lake facies mudstone and coal measure source rocks. According to the comprehensive analysis of petroleum geology, the pre-Jurassic hydrocarbon source rocks in the Shengbei Subsag are not the oil sources of the western crude oil in the Taibei Sag.