Abstract: Based on the analysis of the light hydrocarbons, saturated hydrocarbons and aromatic hydrocarbons from crude oil in Pingbei area of Xihu sag, the C7 light hydrocarbon compound of the Pinghu crude oil are characterized by (1) high methylcyclohexane content, low dimeth?ylcyclopentane and pentane content, and paraffin wax index and heptane value ranging from 3 to 13 and 10%~18%, respectively; (2) wide distribution of carbon number of the n?alkanes without odd?even predominance, the Pr/Ph ratios in most samples distributing between 3.6 and 8.2; (3) steranes mainly consisted of regular sterane, with highest C29 sterane, and relatively high degree of isomerization; (4) relatively high hopane content, the hopane/sterane ratio of 1.5~6.7, low gammacerane content and abundant diterpene; and (5) some Reteneis detected from the aromatic components, the methylphenanthrene index being between 0.71 and 1.42, the highest fluorenehas content among the three series of fluorenecompounds. A comprehensive analysis shows that the oil?forming matrix in Pinghu formation is dominated by terrestrial organic matter, most formed in the oxidation?strong oxidation limnetic facies sedimentary environment, with minority parent material formed in weak oxidizing semi?deep lake facies environment, and the kerogen is mainly in stage of mature to high?mature evolution