30-year-old Satsuma mandarin （Citrus unshiu Marc.） trees grown in acidic and molybdenum （Mo）-deficient orchard soil were used to conduct a two-year field experiment in Yichang City， Hubei Province， China from 2019 to 2021 to achieve scientific application of Mo fertilizer and improve the fruit quality in citrus orchards with Mo-deficiency. 3 treatment groups including the control （CK， foliar spraying with 800 mL water without Mo per plant per application）， treatment group 1 （T1， root drenching with 500 mL of 0.4% sodium molybdate solution per plant per application）， and treatment group 2 （T2， foliar spraying with 800 mL of 0.02% sodium molybdate solutionper plant per application） were set up. All treatments received 1.5 kg of specialized compound fertilizer for citrus （15-7-13） as the basal fertilization. The indexes including the fruit quality， the content of sugar and organic acid components， the activity of antioxidant-related enzymes， and the content of nutrients in fruits and leaves were measured to study the effects of foliar spraying and root drenching with Mo fertilizer on the fruit quality and nutrient utilization efficiency of citrus. The results showed that T1 and T2 significantly increased the parameters of peel color including the value of L^*， a^*， and b^* in Satsuma mandarin fruits in 2021， thereby improving the appearance quality of fruit. T1 and T2 significantly reduced the content of titratable acid （TA） by 16.2% and 22.6 %compared with CK， while increased the content of vitamin C （Vc） by 30.2% and 57.6%， with an improvement in intrinsic quality of the fruit. T1 and T2 significantly decreased the content of citric acid by 33.52% and 20.51%， but the content of malic acid and quinic acid was not significantly affected， indicating that the reduction in the content of TA is mainly attributed to the decrease in the accumulation of citric acid. Mo application significantly enhanced the activity of key enzymes including L-galactono-1，4-lactone dehydrogenase （GLDH）， monodehydroascorbate reductase （MDHAR）， and glutathione reductase （GR） involved in the biosynthesis of ascorbic acid and recycling， while inhibited the activity of ascorbate peroxidase （APX） and ascorbate oxidase （AAO） involved in the degradation of ascorbic acid， indicating that Mo application promotes the biosynthesis and regeneration of ascorbic acid to increase the content of Vc in fruit. T1 increased the ratio of soluble solids to TA and the content of Vc by 24.4% and 30.2%points， and reduced the content of TA by 16.2 %based on the average value of two years. T2 increased the ratio of soluble solids to TA and the content of Vc by 28.6%and 57.6 % while reduced the content of TA by 22.6%， indicating that the performance of T2 is better than that of T1. Overall， root drenching and foliar spraying with Mo fertilizer significantly improved the flavor and nutritional quality of Satsuma mandarin fruits， with effects of foliar spraying better than that of root drenching. It will provide a theoretical basis for the scientific application of Mo fertilizer and the improvement of fruit quality in Mo-deficient citrus orchards in China.