The dynamic change of exporting velocity for C-photosynthate in rice leaves was determined by the analytical technique of nutrient tracer kinetics in living plant. A mathematical model of exporting for photosynthate in the leaves was established. The method of measuring and calculating values of parameters was given

and the parameters for translocation of photosynthate in leaves of rice Xiangaiyou were determined. The results show that the exporting velocity of 14C-photosynthate is adjusted by mutli- factors

and the dynamics of remains and exporting velocity for 14C- photosynthate in rice leaves dose not an follow exact exponential decay process but has some fluctuation characteristics between day and night.