Experimental studies were carried out on the purification of eutrophic Taihu Lake water by dynamic experiment using immobilized nitrogen cycle bacteria (INCB). The results showed that the eutrophic water of Taihu Lake can be purified effectively as it passes through the experimental reactor into which some immobilized nitrogen cycle bacteria were put. The removal efficiencies for Total N (TN), $\mathrm{NH}4+$-N with immobilized nitrogen cycle bacteria were 72.4% and 85.6%, respectively. It was found that the immobilized nitrogen cycle bacteria also have purificatory effect on eutrophic water of Taihu Lake at winter temperature (7°C), and that the removalm efficiencies for Total N (TN), ${\mathrm{NH}}_4^{+}$-N were 55.6%, and 58.9%, respectively. The removal efficiencies for TN and ${\mathrm{NH}}_4^{+}$-N depend on the time the water stays in the experimental reactor.