Based on the analysis of food content and the survey of the composition in fish catches and the data of fish catches in Lake Taihu, the amount changes of catches of Carassius auratus Linnaeus and Their Mutual Relationship with Environment were studied.The results of the survey of fish composition in 2004 and the statistics data of fish catches from 1952 to 2004 showed that:Within recent years, the catches of Carassius auratus Linnaeus had been increasing and had become the second dominant fishes following Coilia ectenes taihuensis Yen et Lin.The a-nalysis of age structure showed that the percentage of 0⁺ fishes increased and the average fish body size decreased.For example, the percentage of 0⁺ Carassius auratus Linnaeus had been increasing according to the trend of y=19.154e^0.0566x(y means the percentage of 0⁺fishes %, x means time a).And the average body length had been decreasing according to the trend of y=115.45e^-0.0312x(y means body size cm, x means time a).The results of food content analysis showed that:the percentage of blue-algae accounted for about 83.65%-93.99% of food volume of Carassius auratus Linnaeus.Under the conditions of eutrophication in Lake Taihu, Carassius auratus Linnaeus mainly fed on blue-algae;eutrophication resulted in the increasing of blue-algae which could be eaten by the fish.The measures of protecting fishes were carried out to ensure the fish propagating.In addition, the trend of percentage of low age fishes increasing and the trend of body size of the fishes decreasing were caused by over-fishing.Carassius auratus Linnaeus might restrain blue-algae increasing because it mainly fed on blue-algae.