The regulation of the carbon-to-nitrogen ratio (C/N) is the core technical feature of biofloc culture. In related research and practice, carbon and nitrogen in C/N have different characterization forms. In this study, dissolved organic carbon (DOC) was used to characterize the organic carbon using total nitrogen (TN), dissolved inorganic nitrogen (DIN), and total ammonia nitrogen (TAN) to characterize nitrogen, respectively, and compare the same C/N under different nitrogen form conditions. The ammonia nitrogen removal capacity, basic nutrient components, functional genes related to nitrogen metabolism, and the total number of heterotrophic bacteria of the lower biofloc were evaluated. In the experiment, the DOC/TN of group A was 20, the DOC/DIN of group B was 20, and the DOC/TAN of group C was 20. In each experimental group, 10 mg/L ammonia nitrogen could be reduced to less than 1 mg/L within 8 hours, and the TAN removal rates were (2.11±0.05) mg TAN/gTSS·h, (2.00±0.02) mgTAN/gTSS·h, and (2.09±0.02) mgTAN/h, respectively. The removal rates of group A was significantly higher than group B (P＜0.05), and there was no significant difference between group C and groups A and B (P＞0.05). There was no significant difference in the crude protein content of flocs among each group. The crude fat content of flocs in group C was significantly higher than that in groups B and A (P＜0.05), and the content of major amino acids and fatty acids was not significantly different (P＞0.05). The abundance of denitrification function genes narG, napA, nirS, and nosZ in flocs in each group ranged from 2.2×10⁶ to 4.7×10⁷ copy/mL. The napA gene in group A was significantly lower than that in group B. The nirS gene was significantly lower than that in group B and C (P＜0.05) and there was no significant difference between group B and group C (P＞0.05). There was no significant difference in the nosZ gene copy factor (P＞0.05). The total number of heterotrophic bacteria and Vibrio in group C were significantly lower than those in groups A and B (P＜0.05). This study shows that adding carbon sources according to different nitrogen forms has an overall effect on the ammonia nitrogen treatment efficiency, function, and nutrient composition of bioflocs within the acceptable range of production. Considering the feasibility of actual operation, it is recommended that the total ammonia nitrogen concentration estimate the amount of carbon source addition required.