Harmful algal blooms are a critical eco-environmental issue with severe impacts on aquatic ecosystems and human health. Tannic acid (TA) has been suggested as an effective algal bloom control, but the molecular mechanisms of its interaction with algae cells and its effects on algal toxin release remain unclear. This study tracked toxin production and release in the toxigenic species Microcystis aeruginosa (M. aeruginosa) exposed to TA, revealing underlying mechanisms through proteomic analysis. High TA doses effectively inhibited M. aeruginosa growth and microcystin-leucine-arginine (MC-LR) production. However, at a specific TA concentration, M. aeruginosa produced and released more MCs, with extracellular MC-LR levels peaking at 1.91 times the control on day 15. Proteomic analysis indicated upregulation of proteins related to the tricarboxylic acid (TCA) cycle, glycolysis, and leucine and arginine biosynthesis, suggesting a compensatory response in M. aeruginosa under TA stress that enhanced cellular energy supply and MC-LR biosynthesis. In addition, TA exposure significantly downregulated proteins involved in ion and metal-cluster binding, disrupting electron transfer and photosynthesis. This study provides new insights into TA-induced MC-pollution risks and TA's mechanisms in algae suppression, offering guidance for its application in algal bloom control.