Abstract: We studied the differentiation process, internal and external morphological changes, and growth positions of flower buds of Deutzia grandiflora Bunge, D. parviflora Bunge, D. scabra Thunb., and D. Schneideriana Rehd. in Beijing by paraffin sectioning and photo measurement. We found that the flower buds of the four species were mainly crown buds and side buds, with summer and autumn differentiation types. Flower bud differentiation was divided into seven periods: undifferentiated, initial differentiation, inflorescence primordial differentiation, flower primordium differentiation, petal primordium differentiation, stamen primordium differentiation, and pistil primordium differentiation periods. The flower organs of each whorl were centripetal, with two types of developmental patterns. Notably, D. scabra and D. Schneideriana were centripetal, while the petals of D. grandiflora and D. parviflora developed earlier than their sepals. Results showed that Deutzia species flourish due to the presence of many buds, high differentiation rate of flower buds, and large number of florets. The longitudinal diameter of flower buds combined with the season accurately reflected the flower bud differentiation period. The pattern of flower organ development supported a close relationship between D. scabra and D. Schneideriana.