Abstract: Analysis on n-alkane carbon isotope curves of oil is an important method for oil-oil and oil-source correlation. The study shows that n-alkane carbon isotope curves tend to be changed due to several secondary actions. Mantle plume event in Permian reformed the oil accumulation conditions, meanwhile the associated abnormal thermal effect brought significant influences to geochemical features and physical-chemical properties of the oil in Tarim basin. Based on the evidences of abnormal thermal effect in Well TZ421, TD2, ZS1(ZS1c) and TZ62 and the analysis of the changes of n-alkane carbon isotope curves of the oil in these wells, it is found that the curves record various abnormal thermal events occurred in Tarim basin and could reflect the reformation of the original carbon isotope characteristics of oil. Through the analysis on the changed n-alkane carbon isotope characteristics caused by abnormal thermal effects, 3 characteristics can be identified, which reflects their differential reformations caused by thermal effects of hydrothermal solution and magma, sulfate thermochemical reduction reaction and thermal alteration, respectively, and reveals the influences of different thermal effects on n-alkane free-carbon isotope fractionation. Using n-alkane carbon isotope characteristics as the basis for marine end-member oil division should be carefully considered in Tarim basin