Abstract: The toxicity mechanisms of soil heavy metal cadmium (Cd) were investigated on seedling growth of Dianthus chinensis and its ascorbic acid-glutathione (AsA-GSH) cycle using concentrations of (0, 0.3, 1, 3, 10, 30 and 50 mg/kg Cd) in the soil in a greenhouse pot experiment. Seedling tiller number, height and biomass exhibited significantly ‘low promoting/suppression’ phenomena. This was because the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and some other antioxidant enzymes increased gradually against increased reactive oxygen species in seedling leaves at low concentrations of soil Cd and at the beginning of the stress. With an increase in Cd concentration and prolonged stress time, the activities of SOD, APX, MDAR, DHAR and GR decreased. This led to the accumulation of excessive reactive oxygen species that could not be removed in an effective way, thus resulting in an outbreak of the superoxide anion (O₂^-·), hydrogen peroxide (H₂O₂), and some other reactive oxygen species, eventually causing membrane lipid peroxidation and stress damage. This work also demonstrated that APX was an important enzyme for H₂O₂ removal, and GR was an important enzyme to generate GSH. It was the main way to renew AsA in the AsA-GSH cycle and restore MDAR to MDHAR.