This study investigated the effects of adding Allium mongolicum Regel flavonoids (AMRF) to the diet on meat quality characteristics of male Saanen kids during post-mortem aging. Eighteen healthy, 3-month-old male dairy goat kids of similar body mass were randomly assigned to a control group (CON) and an AMRF group (2.8 g/(d·kid) of AMRF). The feeding period lasted 139 days, comprising 15 days preliminary period and 124 days experimental period. After completion of the feeding period, longissimus dorsi samples were collected at slaughter, aged at 4 ℃, and measured for physicochemical indicators, textural properties, conventional nutritional components, fatty acid composition, antioxidant capacity, muscle fiber characteristics, ultrastructure, and water mobility after 1, 2 and 3 days. The results showed that during the aging process, the AMRF group exhibited significantly increased redness values and cooked yield compared with the control group (P < 0.05), and the content of polyunsaturated fatty acids in the AMRF group significantly increased with aging time (P < 0.05). Meanwhile, brightness, yellowness, shear force, and cooking loss significantly dropped (P < 0.05). Total antioxidant capacity, superoxide dismutase, and catalase activities significantly increased (P < 0.05), while malondialdehyde content decreased (P < 0.05). Myofibrillar structure remained intact, Z-line degradation was delayed, and the recovery capacity of sarcomere length was enhanced. Low-field nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging (NMRI) revealed superior water-holding capacity in the AMRF group compared with the CON group, with a higher proportion of free water. In summary, dietary supplementation of AMRF effectively enhanced the eating quality and storage characteristics of aged lamb through multiple mechanisms, including enhancing antioxidant capacity, regulating muscle fiber type conversion, improving protein and lipid stability, and optimizing water distribution.