Abstract: On the basis of on-the-spot survey and analysis of water quality in different crab eco-culture sections from April to November of 2004,the influences of crab eco-culture in net-enclosures in East Taihu Lake on water environment were appraised.The results indicate that in the control sections of water resources areas,the main factors which are beyond the standard of fishery water quality are total nitrogen content (TN) and total phosphor content (TP),but in the eco-culture sections the factors over the standard are pH and TP.So the water in the control sections is polluted by nutrient salts.The investigation also indicates that there are a lot of aquatic weeds in the eco-culture sections resulting in that the nutrient contents are much lower than those in the control sections.The results show that the crab eco-culture in net-enclosures in East Taihu Lake does not tamper with the water environment. The water quality in eco-culture sections accords with the demands of “Fishery Water Quality Standards”or“Surface Water Quality Standards Ⅲ”,and is better than that in the comparison sections.