Indoor experiments were performed to determine the accumulation, subcellular distribution, and chemical forms of Cd at five S levels in Hydrilla verticillata. The Cd content increased from 1.229 mg/g to 3.329 mg/g in leaves, and decreased from 2.794 mg/g to 1.023 mg/g in roots, respectively. Excess S supply stimulated Cd assimilation in leaves as Cd accumulation was inhibited in roots. The Cd content in leaves at subcellular levels revealed that Cd was stored mainly in the soluble fraction (71.9-88.2%), and in small quantities in the cell wall (6.1-22.4%) and cell organelles (4.8-6.9%). As S increased, the Cd content in leaf soluble fractions and cell walls increased remarkably. The content of NaCl-extracted Cd in leaves increased as S supply increased, and this parameter was much higher than that of other Cd forms. In leaves, the Cd concentrations in the cell walls were significantly correlated with the chemical forms extracted by HAc, HCl, and NaCl, with correlation coefficients of 0.985, 0.964, and 0.957, respectively. The high correlation indicated that Cd in soluble fractions or cell walls was mainly in the form of pectates/protein, phosphate, and oxalate. The application of S alleviated Cd-induced oxidative stress by increasing the proline accumulation. Furthermore, sulfhydryl proteins such as glutathione and cysteine may play a crucial role in the reversal of Cd-induced oxidative stress.