Flowering is a prerequisite for apple fruiting, and apple flower buds are mixed buds, that is, the vegetative organs and flower structure exist in the same terminal bud simultaneously, which are formed in the year before flowering and fruiting, mainly including spur terminal buds and axillary buds. The infrequent formation of flower buds during its growth and biennial bearing are closely related to flower bud differentiation. Therefore, this paper reviews the research progress of flower bud differentiation of apple from the morphological differentiation, plant hormones and flowering-related genes, in order to provide a theoretical reference for efficient cultivation and stable yield of apple.