In order to study the application potential of ammoniated modified plant tannins in the purification of bloom water,the ammoniated plant tannin flocculant(modified tannin，MT) was synthesized to investigate its algae removal efficiency and its ecotoxicology. At a concentration of 30mg/L，MT achieved a removal rate of 91.4% for bluegreen algae，and 65.35% and 90.53% for ammonia nitrogen and total phosphorus，respectively. In acute toxicity experiments with zebrafish，no mortality was observed，with 96 h LC50＞120mg/L, indicating its low biotoxicity. Subchronic toxicity experiments showed that growth and development indicators (heart rate，hatching rate，survival rate，body length，and deformity rate) for zebrafish larvae exposed to MT were not significantly different from the control group. Further behavioral analysis also demonstrated that the swimming abilities and behaviors of larvae during the exposure and recovery phases remained unchanged，indicating that MT did not adversely affect the nervous system of zebrafish larvae. Additionally，biodegradability tests showed that the modified plant tannin flocculant had a degradation rate of 91% within 28 days，significantly higher than traditional flocculants like polyacrylamide (PAM)，which only achieved 35%，showcasing its superior biodegradability.