Based on the systematic analyses of light hydrocarbon, saturate and aromatic fractions of over 60 oil samples collected from oil fields in the northern and western Qaidam basin, the geochemical characteristics of the oils in the two regions was studied. Based on the calibrating of analytical data of source rocks, identification parameters on age-specific biomarkers for oil source rock age were put forward. The research results show that the oils in northern margin have K1 (Mango's light hydrocarbon parameter) values of around 1. 1, abundant methylcyclohexane and toluene, odd over even w-alkane preference, high Pr/Ph ratios, reflecting the feature of organic matter deposited in Jurassic freshwater lacustrine facies. Whereas, the oils in the western region are characterized by K1 values of almost over 1.2, high abundance of isoalkanes in light hydrocarbons, bimodal n-alkane distribution with odd-to-even (C11~C17) and even-to-odd (C18~C28) predominance, low Pr/Ph, high relative concentration (>30%) of C28sterane, abundant alkyl-chromans (MTTC) with 5, 7, 8-trimethyl-/8-methyl-MTTC ratios<10, indicating the signature of Tertiary saline lacustrine organic matter. Oleanane and norcholestane are believed to be useful age-specific biomarkers for differentiating the oils derived from Jurassic and Tertiary source rocks. Tertiary oils are confirmed by the appearance of oleanane and high 24-/24-+27-norcholestane ratios>0. 6. Jurassic oils lack oleanane and have low 24-/24-+27- norcholestane ratios (<0. 25).