From September to December in 2004, based on the food content investigation, the food relationship and the mutual effects between Coilia ectenes taihuensis Yen et Lin and Hypophthalmichthys molitrix (Cuvier et Valenciennes) and Aristichthys nobilos(Richardson) were studied in Lake Taihu. Results showed that:Cyanobacteria occupied over 90% of food volume in alimentary canal of Hypophthalmichthys molitrix(Cuvier et Valenciennes) and Aristichthys nobilos(Richardson), about 15%-35% of food volume in alimentary canal of Coilia ectenes taihuensis Yen et Lin; Hypophthalmichthys molitrix(Cuvier et Valenciennes) and Aristichthys nobilos(Richardson) basicly fed on the same food. Except Cyanobacteria, Coilia ectenes taihuensis Yen et Lin mainly fed on Cladocera accounting for 89.77% ± 13.69%, Copepoda accounting for 7.84% ± 11.53% and Rotifera accounting for 2.39% ± 4.95%. Hypophthalmichthys molitrix (Cuvier et Valenciennes) and Aristichthys nobilos (Richardson) nearly fed on the same species of Cladocera as that of Coilia ectenes taihuensis Yen et Lin. The partial correlative analysis showed that:there was negative correlation between the catches of Coilia ectenes taihuensis Yen et Linand the catches of Hypophthalmichthys molitrix (Cuvier et Valenciennes) and Aristichthys nobilos (Richardson) at the significant lever of p<0.05.