Allogynogenetic silver crucian carps (Carassius auratus gibelio) were divided into control group and 4 test groups, each group contained 3 replicates by simple factor design. Control group were fed with basal diet, while 4 test groups were fed with basal diet respectively added with 0.25%, 0.50%, 0.75% and 1.00% chitosan oligosaccharide. Two months after feeding under indoor temperature, the fishes were subjected to stress of low temperature, low oxygen and crowd respectively. AKP and SOD activity in liver and glucose content in serum of part of these stressed fishes were determined, and the fishes went through crowd stress were further infected with Aeromonas hydrophila to observe the effect of chitosan oligosaccharide on survive rate of the infected fish. The results showed that glucose content in serum of fishes from test groups with 0.25% to 0.75% of chitosan oligosaccharide decrease under low temperature, low oxygen or crowd stress (P<0.05) and glucose content in fishes from the group with 0.5% of chitosan oligosaccharide decreased mostly, which decreased by 28.06%, 35.28% and 42.01% respectively compared to the control group. AKP and SOD activity in liver of fishes from test groups with 0.50% to 1.00% of chitosan oligosaccharide was increased (P<0.05), those in fishes from groups with 0.5% of chitosan oligosaccharide increased mostly, of which the AKP activity increased by 223.03%, 159.49% and 143.96% respectively under low temperature, low oxygen or crowd stress while the SOD activity increased by 114.90%, 104.78% and 77.39%, compared to the control group. Survive rate of crowded fishes from test groups with 0.50% and 0.75% of chitosan oligosaccharide increased after infection (P<0.05), which increased by 71.42% and 57.12% compared to the control group. In conclusion, a small quantity of chitosan oligosaccharide in diet could enhance anti-stress ability of Carassius auratus gibelio against the environment and the supplement with 0.50% chitosan oligosaccharide in diet is the best.