Macadamia flowers profusely but sheds more than 98% of flowers and fruitlets within 8 weeks after anthesis. There is good evidence for macadamia that girdling fails to ramp up yield despite increasing the early fruit set, but the effect on its physiological mechanism is not well defined. In this study, we applied a 6 mm girdle to the main branches of 6-8 cm diameter at early fruit development, to investigate the effect of main-branch-girdling（MBG） treatment on fruit set and the levels of carbohydrates and endogenous hormones in leaves, bearing shoots and fruit. Results showed that MBG significantly reduced young fruit drop but unchanged the abscission process. Meanwhile, the treatment significantly increased the contents of total soluble sugars and starch in the leaves and bearing shoots, and also enhanced the levels of total soluble sugars included glucose, fructose and sucrose in the husk and seed. These findings suggested that the availability of carbohydrates for fruit retention was improved by MBG. Additionally, MBG increased the indole-3-acetic acid（IAA）, gibberellin（GA₃） and zeatin-riboside（ZR） levels but decreased the abscisic acid（ABA） level in the husk and seed, indicating that MBG reduced the early fruit drop by modifying the balance of endogenous hormones. Therefore, a positive interplay between carbohydrates and endogenous hormones was involved in the reduction of early fruit abscission induced by MBG in macadamia.