Abstract: We investigated the effect of exogenous Ca or K on the growth and physiological parameters of Arabidopsis thaliana seedlings under different levels of Cd stress (0, 20, 40, 60 and 80 μmol·L^–1). The optimal alleviation concentration for Ca²⁺ was 10 mmol·L^–1 under all levels of Cd stress in terms of root growth and biomass of seedlings. The optimal alleviation concentration for K⁺ was 10 mmol·L^–1 under low Cd stress (20 and 40 μmol·L^–1) and 20 mmol·L^–1 under high Cd stress (60 and 80 μmol·L^–1). Under low Cd treatment, the exogenous addition of Ca or K with the optimal concentration resulted in recovered root growth and increased biomass, with no change in superoxide dismutase (SOD) activity, soluble protein content or malony dialdehyde (MDA) content of seedlings. The addition of Ca or K significantly decreased peroxidase (POD) activity and decreased total phenol, flavonoid, anthocyanin, total acid thiol, glutathione (GSH) and phytochelatins (PCs). Under high Cd stress, the exogenous addition of the optimal concentration of Ca²⁺ or K⁺ increased SOD activity and decreased POD activity. The addition of Ca or K significantly decreased levels of soluble protein, MDA, total phenol, flavonoid, anthocyanin, total acid thiol, GSH and PCs. Under all levels of Cd, the TT pyrimidine dimer contents were higher in the seedlings without than with Ca and K (P<0.05), so the DNA damage in seedlings was alleviated by the addition of Ca or K. Exogenous addition of Ca or K can alleviate the toxicity of Cd in Arabidopsis seedlings, especially under high Cd stress, by mediating the metabolic levels of antioxidants, osmotic adjust substance, phenols and metal chelating substances, thus reducing DNA damage in cells. This study provides experimental data for the molecular mechanisms involving the alleviation effects of Ca and K on heavy metals and valuable references for the application of Ca and K in the remediation of heavy metal pollution.