Experimental studies were carried outon the purification of eut rophic lake water by simulative dy namic experiment using immobilized nit rogen cy cle bacteria.The results showed that the eut rophic water of Taihu Lake can be purified ef fectively as it pass through dif ferent immobilized nit rogen cy cle bacteria zones.The removal eff iciencies for Total N (TN), NH₄⁺-N with immobilized nit rogen cycle bacteria were 72.4% and 85.6%, respectively.It was found that the immobilized nit rogen cycle bacteria also have purificatory effecton eut rophic water of Taihu lake in winter (7℃), the removal ef ficiencies for Total N (TN), NH₄⁺-N were 55.6%, and 58.9%, respectively.The removal ef ficiencies for TN and NH₄⁺-N depended on the retention time of the water in eximperimental zone.