Abstract: Biofloc technology used in shrimp and tilapia aquaculture reflects the feed coefficient decreased water quality environment to improve and accelerate the growth of the combined effect of the technology widely farmed in China cyprinids how the application effect has not been reported. Study of different C/N level of the bioflocs formation, water quality and growth of grass carp. A locally formulated and prepared feed containing 30% crude protein with C/N ratio 10.8 was applied to all ponds. In order to raise the C/N ratio of the feed input to 15, 20 and 25, glucose was applied separately as a source of carbohydrate in addition to the artificial feed. The results show that when the C/N is over 15, the biofloc can effectively regulate water quality, reduce water of ammonia, nitrite concentration; each group the biofloc volume the index (FVI) with gradual increase in breeding time, stabilized in Rule 14d; With the C/N increased, the biofloc groups formed in the water content of crude protein was significantly higher (P <0.05) than control groups, but the growth of grass carp shows a decreasing trend. Overall, biofloc technology used in the breeding of grass carp appropriate C/N of 15, the ratio can promote the biofloc formation, and can effectively reduce ammonia nitrogen, nitrite nitrogen levels.