Diethyl aminoethyl hexanoate （DA-6） is an efficient plant growth regulator that can regulate the physiological metabolism in fruit and improve the fruit quality.Citrus reticulata ‘Huagan No.2’ （Ponkan） was used to study the effects of DA-6 on the fruit quality in citrus.A foliar spray of 30 mg/L DA-6 was applied at the late stage of fruit expansion.Fruit quality and the expression of key genes involved in the synthesis，degradation，and transport of sugars and organic acids were systematically analyzed to elucidate the molecular mechanisms underlying the DA-6-mediated regulation of the accumulation of sugar and organic acid in citrus fruits.The results showed that the single fruit weight，peel color index （a^*），the content of total soluble solids，sucrose，fructose，and glucose after the DA-6 treatment of 30 and 60 days were significantly increased，while the content of titratable acidity and citric acid were significantly decreased.DA-6 treatment significantly upregulated the expression of sucrose transport-related genes （SUT1，SUT2，and VPP-1），cell wall invertase genes （CWINV1，CWINV2，CWINV4，CWINV5，and CWINV6），vacuolar invertase gene （VINV），and sucrose phosphate synthase genes （SPS1，SPS2，and SPS3） in juice sacs.The expression level of genes involved in the synthesis of citric acid （CS2，PEPC1，PEPC2，PEPC3） and vacuolar proton pump-related genes （VHA-F2，VHA-c4） was significantly downregulated，whereas the expression level of genes involved in the degradation of citric acid （ACO1，ACO2，ACO3，ACLα1，ACLα2） was significantly upregulated.It is indicated that DA-6 treatment enhances the strength of sink in fruit juice sacs，promotes the synthesis of sucrose，transmembrane transport，and vacuolar metabolism to increase the accumulation of sugar，simultaneously inhibiting the synthesis and transport of citric acid and promoting its degradation，thereby reducing the accumulation of citric acid and ultimately improving the fruit quality in citrus by increasing the content of sugar and decreasing the content of titratable acidity in fruits.