In order to study the effects of biofloc on water quality and metabolic functions of microbial community in zero-water exchange tanks, glucose was used as carbon source, and water quality and carbon metabolic diversity of microbial community were investigated based on Biolog-ECO plates. The results showed that: mature biofloc reduced effectively the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen (P<0.05) and meanwhile significantly improved the content of total suspended solids (TSS). Average well color development (AWCD) reached stationary phase after 108h cultivation in control and floc treatments, and the floc treatment was 18% higher than that in control group. The utilization of polymers and carbohydrates in biofloc tanks were improved. Meanwhile, the diversity indexes (Shannon index, richness index) of the biofloc tanks were higher than those of control group (P<0.05). The principal component analysis of microbial metabolic characteristics in two treatments showed that principal components 1 (PC1) accounted for 66.9%, and principal components 2 (PC2) accounted for 12.4% respectively. Significant differences in carbon metabolic characteristics of microbial community in the culture water were found between floc treatment and control group. Thus, biofloc technology effectively reduces the nitrogen content, and improves the metabolic activity of microbial community, and also influences the function of microbial community in the culture water.