Abstract: Atriplex centralasiatica is a typical halophyte that widely grows in saline areas of China. In earlier studies, we found that salt stress markedly induced the accumulation of flavonoid in the roots of A. centralasiatica seedlings. By integrating the physiological and biochemical analyses in this study, the physiological mechanisms of salt-induced flavonoid accumulation in the roots of A. centralasiatica seedlings were investigated by supplementing with KNO₃ (25 and 35 mmol·L^-1) and exogenous quercetin (100 nmol·L^-1 quercetin) in different salinity-treated seedlings (50, 100, 250, 500 and 600 mmol·L^-1 NaCl). Our results indicated that supplementation of exogenous quercetin markedly suppressed primary root (PR) growth and the accumulation of both H₂O₂ and MDA in roots, whereas it markedly increased soluble sugar levels in seedlings. This indicated that exogenous flavonoid-quercetin affected root system architecture by suppressing PR growth and improved salt tolerance by reducing oxidative damage in A. centralasiatica seedlings. Salt stress also induced the accumulation of nitrate (NO₃^-) in A. centralasiatica seedlings. We found that treatment with 25 and 35 mmol·L^-1 KNO₃ markedly induced the accumulation of flavonoid in root tips of A. centralasiatica seedlings. All in all, the results indicated that nitrate modulated salt tolerance in A. centralasiatica seedlings by flavonoid pathway. This knowledge was helpful for further elucidating the physiological and molecular mechanisms of salt tolerance in A. centralasiatica. It also provided further insights into novel strategies for breeding and cultivating salt-tolerant crops and improved saline-alkali soils using modern biotechnology and agricultural measure.