Abstract: This study investigated the effects of Cd²⁺ on the biomass, chlorophyll a content, phycoerythrin content and ATP content, the maximum quantum yield of PSII (F_v/F_m), the effective photochemical yield of PSII (YII), the relative electron transfer rate (ETR) and non-photochemical fluorescence of quenching (NPQ) of the Porphyridium purpureum. The results showed that the growth rate of P. purpureum decreased significantly by the stress of Cd²⁺ in a dosage-dependent pattern. The content of chlorophyll a, phycoerythrin and ATP decreased significantly by Cd²⁺ stress with a dose-dependent way. The chlorophyll fluorescence parameters (F_v/F_m, YII and ETR) under Cd²⁺ stress were significantly lower than those of the control groups and decreased rapidly with increased Cd²⁺ concentration. NPQ value increased significantly at low Cd²⁺ (<200 μmol/L) and decreased significantly at high Cd²⁺ (>500 μmol/L). Therefore, the gorwth and phtochemical activities ofPorphyridium purpureum would be significantly affected by the concentration of the Cd²⁺ above 5 μmol/L and the accumulation of Cd²⁺ would have an impact on the ecological balance of the Porphyridium purpureum in aquatic environment.