Abstract: To enhance the fruit quality of early-ripening Satsuma mandarin “Xingjin”, this study focused on the significant metabolic pathway of plant photosynthesis, namely “porphyrin and chlorophyll metabolism”, and screened the amino acid precursor substances, glutamate and aminolevulinic acid, which play crucial roles in the chlorophyll synthesis process. Taking Xingjin early-ripening Satsuma mandarin from Huaning County, Yunnan Province as the material, five distinct spraying amino acid foliar fertilizer treatments（CK, T₁, T₂, T₃, and T₄） were established. The physiological indicators of leaf metabolism, enzyme activities, and gene expression levels from July 9 th to September 27 th, and the physiological indicators of fruit quality on September 27 th（maturity stage） were determined. The regulation of chlorophyll biosynthesis in citrus leaves and the formation of fruit quality was explored. The results indicated that foliar spraying of amino acid fertilizer could promote chlorophyll synthesis in Xingjin leaves, fruit color change, and acid reduction. Among them, T₃ treatment had the best effect in promoting fruit quality improvement. This research offers an alternative fertilization plan for the fruiting period of early-ripening Xingjin.