Abstract: The dynamic changes of total phenol content, total flavonoid content and total phenolic acid content in Fortunella crassifolia during the fruit development were studied. The contents of total phenols, total flavonoids and total phenolic acids in Fortunella crassifolia fruit at different growth stages were determined and analyzed by using the variety of kumquat in Youxi as the experimental material. The results showed that:the contents of total flavonoids and total phenolic acids in the fruit of kumquat decreased sharply with the increase of maturity at 55-65 days after flowering, and changed gently at around 85 days after flowering, and then at about 125 days after flowering, the flavonoid content and phenolic acid content increased slightly and then decreased after 125 days after flowering; The flavonoid content and phenolic acid content in the pericarp was higher than that in the flesh. The fruit of kumquat was rich in phenolic substance and it tended to decrease with the growth and development of the fruit. The content of total phenols and flavonoids in the fruit of kumquat was positively correlated. The young fruit of kumquat had higher phenolic substance and stronger antioxidant ability than the ripe fruit.