<p>Arsenic (As) pollution in mining areas has become a critical global environmental issue. In particular, the excessive accumulation of As(V) in edible plants has raised significant concerns for food safety and human health. However, the mechanisms by which different concentrations of ferrous ion (Fe²⁺) influence phytotoxicity, As(V) uptake, and related metabolic processes remain unclear. In this study, we found that As(V) exposure significantly reduced biomass, root length, photosynthetic pigments and Fe content of <i>Brassica chinensis</i> L., inhibiting overall growth and development of the plant. As(V) triggered oxidative stress by generating excessive reactive oxygen species (ROS), which disrupted cellular homeostasis. Exogenous Fe²⁺ treatment, especially at 50 µmol/L, markedly enhanced the activities of key antioxidant enzymes, including SOD and POD, effectively mitigating oxidative damage. In addition, Fe²⁺ restricted As(V) uptake by promoting the formation of an adsorbed iron oxide film on the root surface and was associated with reduced expression of PHT1;4 in root tissues. Metabolomic analysis further demonstrated that Fe²⁺ treatment was associated with enhanced flavonoid biosynthesis pathways and increased accumulation of flavonoids under As(V) stress, which may contribute to improving plant tolerance. These findings underscore the protective role of Fe²⁺ against As(V) toxicity in <i>Brassica chinensis</i> L. and provide a potential strategy for mitigating risks to human food safety caused by As(V) contamination.</p>