[en] Analysis method of in individual molecule hydrocarbon carbon isotopic compositions of crude oil and sediment extracts is introduced in this paper. Through contrast measure of individual molecule δ C values in pretreated alkanes sample and origin alkanes sample, and in n-alkanes standard sample and its mixture with i-alkanes, and discuss on three routine baseline pattern data treat method, error sources of individual molecule hydrocarbon carbon isotopic compositions were analysis. It was illustrated that sample pretreatment of separating n-alkanes from i-alkanes, chromatogram temperature program and data treat have significant effects on the δ C values of individual molecule hydrocarbon. It is point out that beforehand sample treat of separating n-alkanes from i-alkanes with urea complex or 5A molecule sift adsorption, using single temperature rate or keep lower temperature grads during the compound flow out and the subsection date treat for multi-inflexion baseline pattern can improve the precision and accuracy of measure. (authors)