Based on the catches from 1973 to 2002 and an investigation of age structure and food composition of lake anchovy (Coilia ectenes taihuensis Yen et Lin) in 2004, the reasons of the fish catches increasing in Lake Taihu were analyzed in mutual relation to the biological environmental factors. The results showed that:since 1994 the catches of lake anchovy had been increasing annually at the rate of 1430 ton;0⁺ individuals accounted for 99.04±2.21% in 2003 and 99.08±0.80% in 2004 of total individuals in its catches; 0⁺ lake anchovy entirely feed on zooplankton, among which the percentage of Cladocera in 0⁺ the fish food was 89.77±13.69%. The analysis showed that:the relationship between the catches of the fish and TIN, TN and COD showed positive correlation at the significant level of P<0.05; the relationship between the catches of the fish and the catches of topmouth culter (Erythroculter ilishaeformis Bleek) and ice fish (taihuensis Chen) showed negative correlation at the very significant level of P<0.01; the trend of low age composition in the fish population was conform with the increasing of fishing intensity of the lake in recenl years. With the increasing of lake anchovy catches, there was decreasing trend of zooplankton standing crop.