Abstract: 【Objective】 The objective of this study is to study the relationship between external morphology and internal anatomical structure of flower buds during flower bud differentiation, and the relationship between hormones content and flower bud differentiation in Xanthoceras sorbifolium Bunge. The results will provide reference for the timely sampling in the study of X. sorbifolium Bunge flower sex and the regulation techniques used to increase the ratio of female to male flowers. 【Method】 Through the external morphology observation, combined with the paraffin sections, the correspondence between the internal and external morphology of the flower bud differentiation process was analyzed. To study the relationship between hormones content and flower bud differentiation in X. sorbifolium Bunge, four kinds of endogenous hormones in female flowers and male flowers were determined by HPLC. 【Result】 Both the female flowers and male flowers were bisexual before sex differentiation. There was vacuolization in mononuclear pollen grains during mitosis stage in female flowers, and the megaspore mother cell stopped dividing during the tetrad stage in male flowers. As a result, the abnormal development of sexual organs caused the formation of a unisexual flower. In addition, there was a temporal correspondence between the internal structure and the external morphology of flower buds. The zeatin(ZT)content increased gradually during the stage from flower bud undifferentiated period to pistil primordium differentiation. During male and female gametophyte formation period, the ZT content of female flowers was always higher than those of the male flowers. The IAA and ABA contents of female flowers were significantly higher than those of the male flowers when the stamens of female flowers developed abnormally, and the GA content was significantly lower than those of the male flowers. It is indicated that high levels of ZT can promote flower bud differentiation, and was beneficial to the development of female flowers. High levels of the IAA and ABA had a promoting effect on female flowers formation, and high levels of the GA promoted the development of male flowers. The ratios of m(ABA)to m(IAA), m(ABA)to m(GA), and m(ZT)to m(GA)were at a high level during the period from flower bud undifferentiated period to pistil primordium differentiation. When male flower pistil dysplasia was abnormal, the ratios of m(ABA)to m(IAA)and m(ZT)to m(IAA)of male flowers were significantly higher than that in females, indicating that high levels of the ratios of m(ABA)to m(IAA), m(ABA)to m(GA), and m(ZT)to m(GA)were beneficial to flower bud differentiation; and high levels ratio of m(ABA)to m(IAA)and m(ZT)to m(IAA)were beneficial to stamen development. 【Conclusion】 The abortion of the other sexual organ lead to the formation of female and male flowers in X.anthoceras sorbifolium. The internal differentiation period can be judged based on the external morphology during the flower bud differentiation. High levels of the ZT, m(ABA)/m(IAA), m(ABA)/m(GA), and m(ZT)/m(GA)are beneficial for flower bud differentiation. High levels of the ZT, IAA and ABA are beneficial for female flower development, and high levels of the GA, the ratios of m(ABA)to m(IAA)and m(ZT)to m(IAA)are beneficial for male flower development.