Abstract: Use annual cuttings Bougainvillea spectabilis ‘Crimelake’ as the experimental material, makes permanent slices by means of conventional paraffin method, research of the flower bud differentiation process by the microscopic observation; The correlation between them is established by observe the external morphology, record and analysis the change rule of bud at the same time. The results show that the flower bud differentiation of B. spectabilis stared at the early of August, and ended at the beginning of September, until mid to late October reaches into the full-bloom stage; B. spectabilis flower bud differentiation process can be divided into 8 periods: vegetative growth, formative stage of inflorescence primordium, formative stage of bract primordium, formative stage of floret primordium, formative stage of sepal primordium , formative stage of petal primordium, formative stage of stamen and pistil primordium; It is difficult to judge the differentiation process from the appearance, as the flower bud changes is not obvious and small in the early stage of flower bud differentiation, and the later differentiation speed is accelerate, showing the apparent elongation and swelling; The flower bud of B. spectabilis is axillary pure bud, there is a certain crossover between different differentiation stages, and continuous differentiation develops into complete umbellate inflorescence. In conclusion, the flower bud differentiation maintains 1 month, about 8 stages, the external morphological change is not obvious at the prophase of flower bud differentiation, can’t intuitive reflect its internal structure change, the differentiation speed is accelerate, and change obviously, can intuitively judge the flower bud differentiation process from the external form.