Antibiotics and heavy metals are persistent pollutants in the environment， and the assessment of their toxicity to organisms has always been a hotspot of study. This article investigated the effects of single and combined pollution of tetracycline/sulfamethoxazole and cadmium ions on the growth of Synechocystis sp. PCC6803. The results showed that a single exposure to 100 ng/L sulfamethoxazole（SMX） stimulated the growth and photosynthetic activity of Synechocystis， whereas treatment with tetracycline（TC） had no significant effect. Cadmium ions（Cd²⁺） at 0.001 mg/L did not significantly affect the physiology of Synechocystis， but Cd²⁺ at 0.5 mg/L significantly inhibited the growth and photosynthesis of Synechocystis. This concentration downregulated photosynthesis-related gene（psbA2）， disrupted the antioxidant system of Synechocystis， damaged its cell membranes， and stimulated the secretion of its extracellular polysaccharides. When 100 ng/L TC coexisted with 0.001 mg/L Cd²⁺ synergistically， the cellular esterase activity was stimulated. 100 ng/L SMX alleviated oxidative damage caused by 0.5 mg/L Cd²⁺， resulting in the reduced production of reactive oxygen species（ROS）， the decreased activity of superoxide dismutase（SOD）， and the low content of malonaldehyde（MDA） compared to the group treated by single 0.5 mg/L Cd²⁺. When both were present simultaneously， they synergistically stimulated the activity of esterase in Synechocystis. Low concentrations of tetracycline had minimal impact on cell growth and did not significantly alter the cytotoxicity of Cd²⁺ on cells. In contrast， low concentrations of sulfamethoxazole promoted cell growth and mitigated the cytotoxic effects of Cd²⁺ on cells. It is indicated that it is necessary to comprehensively consider the combined pollution of antibiotics and heavy metals when pollution is assessed.