To explore the effects of pruning measures on the endogenous hormone contents, carbon and nitrogen nutrition contents in Purpleleaf Lagerstroemia indica flower buds of secondary flowering, and provide a theoretical basis for florescence regulation, we took L. indica ‘Ebony Embers’ as experimental materials in this study. The severe pruning were carried out on main flowering branches in late flowering period with no pruning as control. The changes of indole acetic acid (IAA), abscisic acid (ABA), gibberellin (GA₃), zeatin riboside (ZR), soluble sugar, starch and total nitrogen contents in flower buds of Purpleleaf L. indica under different treatments were analyzed. The results showed that: (1) the content of endogenous ZR in flower buds of Purpleleaf L. indica increased significantly at each flower development stage after pruning. The content of endogenous GA₃ decreased at the stage of flower bud differentiation, and increased significantly from the initial flowering stage to the late flowering stage after pruning. The endogenous IAA content increased significantly at the stage of flower bud differentiation, and decreased from the initial flowering stage to the late flowering stage after pruning. The endogenous ABA content did not change significantly after pruning. (2) The content of soluble sugar in flower buds of Purpleleaf L. indica increased at first and then decreased after pruning, and reached a significant level at the late flowering stage. The content of starch and total nitrogen increased, while the difference was not significant. (3) The C/N ratio in flower buds of Purpleleaf L. indica in general, and the C/N ratio increased slightly after pruning. The study argued that pruning affects the endogenous hormone levels of Purpleleaf L. indica, and effects the metabolism of carbon and nitrogen nutrition in flower buds by regulating the contents of carbohydrate and total nitrogen. Pruning promotes the secondary flowering and prolongs the blooming period of Purpleleaf L. indica.