In order to enhance the safety of the bioflocculation technology, the accumulation of the feed-source copper Cu (II) and effect of Cu (II) on the ammonia oxidation about a nitrification bioflocculation in the aquaculture system was experimentally investigated. The concentration of Cu (II) in the culture water as well as the concentration contained in the flocs of the biofloc aquaculture system were determined, respectively. The results showed that the Cu (II) content in the breeding system was increasing with the feed feeding, reaching μg/L (18.34 ± 0.77) after 91 d, and the Cu (II) content in the catkins did not accumulate significantly at 91 d. After washing the above cultured floc with deionized water, 0, 25, 50, 100, 250, 500, 1000 μg·L-1 Cu (II) were added to each group and simultaneously adding NH4Cl, which served as a reaction substrate for the ammonia oxidation process.  At the end of the study, it was found that the ammonia oxidation rate for each group was above 0.44 mg·(L h)-1 and the removal rate of ammonia nitrogen was above 97% in 20 h. The results showed that the concentration of Cu (II) in the water continued to accumulate with the feeding regime, but that of flocs did not accumulate during the 91-day period. Most importantly, it was found that even if Cu (II) in the system reached 1000 μg·L-1, it would not significantly affect the effect of ammonia oxidation.