We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last ~21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ13C of organic matter and summer monsoon variations. The change in δ13C values of organic matter (in accordance with the ratios of C3 to C4 plants) results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ13C values of organic matter and the local climate system.