Abstract: This paper presents a systematic review on the photosynthetic ways and fractionation processes of organic carbon isotope of terrestrial plants as well as on the influences of temperature, illumination, atmospheric CO₂ concentration and moisture on the fractionation of organic carbon isotope. Based on analyses of the relation of soil organic carbon isotopes with the vegetation types, applications of organic carbon isotope to paleoenvironmental research were introduced. In view of the problems currently existing in the study of organic carbon isotope, we suggest that more attention should be paid both to the improvement of experimental technology and to the analysis of modern processes in the future work so as to yield more reasonable and accurate explanations of the organic carbon isotopes from paleoenvironmental records.