The effects of poly-γ-glutamic acid (PGA) aqueous solution irrigation on seedlings trait and resistance-related enzymes in leaves of citrus were determined by measuring plant height,crown diameter and enzyme activity. HILIC LC-MS/MS was used to analyze the changes of 200 target metabolites in leaves after irrigation of PGA. The results showed that PGA treatment increased the height,crown diameter and branch number of seedlings. The activities of superoxide dismutase (SOD),peroxidase (POD) and polyphenol oxidase (PPO) in citrus leaves were increased after PGA treatment. The content of L-glutamate in citrus leaves decreased by 73.2%,while the content of γ-aminobutyric acid (GABA) increased by 1.6 times. The content of N6-methyl adenine increased by 2.3 times.The results of quantities of 109 metabolites analyzed by targeted metabolite showed that the difference of 13 metabolites between control and treatment was significant.