Abstract: To study the effects of different carbon-nitrogen ratios on biofloc formation and the speed of growth, intestinal digestive enzymes and hepatopancreatic antioxidant enzymes of Macrobrachium nipponense, five different experimental groups were set up control group (no carbon source added), carbon-nitrogen ratio 10 (C/N10), carbon-nitrogen ratio 15 (C/N15), carbon-nitrogen ratio 20 (C/N20) and carbon-nitrogen ratio 25 (C/N25) with three replicates per group. The original weight (0.25±0.03) g of Macrobrachium nipponense were cultured in a glass jar (30 cm×40 cm×100 cm) for 50 days. The results showed that the content of bio-flocs increased with the increase of C/N ratio. The content grades of bio-flocs ranking were C/N20, C/N25, C/N15 and C/N10, of which C/N20 had the largest bio-flocs. The volume of bio-flocs and total solid suspended matter were 328.67 (+7.09 mL/L) and 40.33 (+1.53 mg/L), while C/N10 group had almost no bio-flocs. C/N15 and C/N25 groups had some bio-flocs, but the content was significantly lower than that of C/N20. The concentration of ammonia nitrogen and nitrite nitrogen in the control group continued to increase. The concentration of ammonia nitrogen and nitrite nitrogen in C/N10 and C/N25 groups fluctuated greatly, showing a trend of first increase, then decrease, and then increase. The concentration of ammonia nitrogen and nitrite nitrogen were higher than 2 mg/L and 1.5 mg/L, respectively. The concentration of ammonia nitrogen and nitrite nitrogen in C/N15 and C/N20 groups maintained at low level without sharp fluctuation during the whole culture period, while the concentration were lower than 0.35 mg/L and 0.6 mg/L, respectively. The weight gain rate was C/N20>C/N25>C/N15>C/N10>control group, which was 29.69%, 50.22%, 89.52%, 75.98% and higher than the control group, respectively (P<0.05). The specific growth rate was C/N20>C/N25>C/N15>C/N10>control group, which was 18.41%, 24.69%, 42.26%, 33.89% and higher than the control group respectively (P<0.05). In terms of antioxidant enzymes, GPX activity was C/N20>C/N25>C/N15 >C/N10>control, which was 1.70%, 21.42%, 43.19%, 31.49% and higher than the control group (P<0.05). Superoxide dismutase (SOD) activity was ranked by C/N20>C/N25>C/N15>C/N10>control group, which was 73.35%, 47.12%, 35.26%, 19.34% and higher than the control group, respectively. In terms of digestive enzymes, amylase activity was C/N20>C/N15>C/N25>control>C/N10, which was 68.09%, 231.91%, 42.55% and higher than the control group, respectively (P<0.05). Lipase activity was ranking as C/N20>C/N25>C/N15>control>C/N10, which was 2.86%, 25.45%, 23.12% and higher than the control group (P<0.05). The activity of trypsin was C/N20>C/N25>C/N15>C/N10>control, which was 12.98%, 14.52%, 36.45%, 24.63% and higher than the control group (P<0.05). The results suggested that bio-flocs can be effectively produced when the C/N ratio is 20 under the culture condition, and the concentration of ammonia nitrogen and nitrite nitrogen in the water environment was able to be reduced greatly. In addition, the growth performance, intestinal digestive enzyme activity and hepatopancreatic antioxidant enzyme activity of Macrobrachium nipponensis can be significantly improved.