Abstract: The processes of flower bud differentiation and the changes of photosynthetic characteristics，carbohydrates，soluble proteins and hormones were studied during flower bud development in Phalaenopsis‘Big Chili’. The results showed that flower bud differentiation could be divided into initial differentiation stage，inflorescence primordium differentiation stage，flower primordium differentiation stage，sepal primordium differentiation stage and petal primordium differentiation stage（16 cm and 24 cm），when the length of spike was 0，2，4，8，16 and 24 cm，respectively. The net CO2 uptake rate of Phalaenopsis showed no significant difference in the early stage of flower bud differentiation（0–4 cm），while the rate was markedly reduced in the spike at 8 cm in length. The contents of carbohydrates and soluble proteins in flower buds were significantly higher than those in leaves. The carbohydrate level reached a steady state when the length of flower bud was 4 cm and the contents of soluble proteins achieved a balance between leaves and flower buds when the flower bud grew to 8 cm. The contents of GA in the flower bud reached the maximum level in the inflorescence primordium differentiation stage（2 cm）. IAA levels increased significantly when the flower bud grew to 4 cm，and ZT contents strongly decreased in the flower bud at 8 cm in length，while the contents of ABA showed no significant change during the whole process of flower bud differentiation. In conclusion，the photosynthetic，physiological and biochemical characteristics reached a relatively stable level when the sepal primordium began to differentiate（8 cm），and floral determination was likely to have been completely finished at this stage.

Key words: Phalaenopsis, microstructure, net CO2 uptake rate, carbohydrate