Marine macroalgae are enriched in heavy metals, and the enrichment of heavy metals by macroalgae is driven by concentration differences, binding of heavy metals to the cell surface of algae, and active uptake of heavy metals by algae. The enrichment of heavy metals by algae is affected by a variety of environmental factors including pH, temperature, salinity, etc., in addition to the type and concentration of heavy metals and the type of algae. Based on the investigation of heavy metal content in seaweeds by domestic and foreign scholars, this review summarizes the environmental effects of heavy metal-enriched seaweeds. On the one hand, the biomagnification of heavy metals along the food chain may cause ecological hazards and human health threats. On the other hand, the use of macroalgae as indicator organisms for heavy metal pollution in seawater or bioremediation materials for heavy metal pollution in water bodies has received increasingly widespread attention by taking advantage of the differences in the enrichment of heavy metals by seaweeds.