Abstract: To investigate the effects of flower bud differentiation on photosynthesis and assimilation products， we analyzed the variation in the concentrations of leaf photosynthesis，carbon and nitrogen metabolism of‘ Feizixiao’ litchi trees. The results showed that Photosynthesis（ Pn，2.39 μmol/m2·s） was significantly higher in flowering shoot than that in vegetative shoot（ 1.60 μmol/m2·s）. In addition，it was found that the stomatal conductance （Gs），internal CO2 concentration（ Ci），transpiration rate（ Tr），and water use efficiency（ WUE） of flowering shoot were higher than those of vegetative shoot. During the flower bud differentiation stage，the contents of soluble sugars and C/N ratio of flowering shoot were significantly higher than those of vegetative shoot，whereas total nitrogen had a contrary tendency. The results suggested that there was higher potential photosynthetic capacity in flowering shoot than that in vegetative shoot. Litchi flowering was able to promote assimilation production，more sugar gave out a rich basis for the development of flower buds and to keep floral formation moving along smoothly.