The stable isotope composition of land snail shell fossil is correlated with the paleo-environmental information, and therefore could be used to reconstruct the palaeo-environment. However, the debate continues on the mechanism how paleo-environment factors affect the stable isotope composition of snail shell carbonate. Recent studies focus more on the δ13C value of the modern land snail shell carbonate which could be applied to indicate the environmental and climatic information. The laboratory cultured experiment can isolate the contribution of each particular environmental factor to the δ13C value of the snail shell carbonate. In this study, the cultured experiments on the snail Achatina fulica were carried out to investigate the carbon isotope fractionation between snail shell carbonate and their diets，The results show that under constant temperature and humidity there are stable fractionation offsets among the shell carbonates when the snails were fed by the same diet. The different types of diets caused the correspondingly different carbon isotope fractionation: the average fractionation offsets between the shell carbonate and the diets of the lettuce, the corn and the forage are 16.70‰±0.2‰, 10.57‰±0.2‰, 10.65‰±0.2‰, respectively. The experiment also confirms that the incubators temperature ranging from 20 to 30oC does not affect thefractionation offset of 13C between the snail shell and its diet. An empirical equation between the δ13C values from the shell carbonate ofAchatina fulica and the diets can be described as δ13Cs=0.6665δ13Cv+6.2302 (n=26). The inorganic carbonate has negligible effect on the δ13C value of snail shell. According to the result of the end-member analysis, we concluded that the diet contributes dominantly to the carbon stable isotope composition of the shell carbonate of snail Achatina fulica with the contribution being about 80％±5％, and the another one, i.e, from the atmospheric CO2 , being 20％±5％.