CH4 emission is an interaction result of CH4 production, oxidation and transport in rice paddy field. CH4 emits into the atmosphere primarily through the following three channels: liquid diffusion, bubble and plant aerenchyma. The relative contributions of the three pathways to CH4 emission varies according to organic loading, rice cultivar, rice planting density, seasonal variation in temperature, etc. A large number of researches indicated that CH4 generated in paddy soils mostly emitted into the atmosphere through the aerenchyma of rice plants. The application of stable carbon isotope technique to investigate CH4 transport through the aerenchyma of rice plants found that isotope fractionation existed in the process of CH4 transport. It is reported that there are two ways to calculate isotope fractionation factor e transport of CH4 transport, and the results obtained in the two ways (-18‰ ~ -9‰) are quite approximate. But previous research methods have some defects, which may affect the accuracy of the results. Furthermore there lacks of model about CH4 transport in paddy soil.