Abstract: The paper aims to solve the problem of almost no blooming flower or close flower after pruning on Hydrangea macrophyflla. The experiment was carried out on H. macrophyflla‘Classic red’. The morphological development of flower buds was observed by scanning electron microscope. After completing the flower bud differentiation, the plants were cultivated to observe the floral development and bloom. The correlation between temperature and floral evocation was analyzed. The results showed that the process of flower bud differentiation was divided into five stages: the vegetative stage, inflorescence stage, meristem division stage, differentiation of floral primordia stage and differentiation of floral organs stage. H. macrophyflla treated at different times with low temperature could promote flowering, but the plants without vernalization had influence on the quality of flowers. H. macrophyflla completed the flower bud differentiation process for about four months, and the bud differentiation process had a significant correlation with temperature, the growth point expansion was at 20- 25℃, the meristematic doms was at 15-20℃, the floral primordium was formed at 10℃ and the floral organs were formed and the dormancy was broken at 5℃.