With the development of aquaculture industry and the community’s increasing attention to environmental protection,aquaculture wastewater reuse has become an inevitable trend.As a key factor in aquaculture wastewater treatment,hydraulic condition plays critical roles in biofilm growth and water flow pattern within the reactors.Researching the relationship between biofilm growth and water flow pattern will be conducive to improve the efficiency of wastewater treatment.In the present study,aiming to know the effect of flow velocity on biofilm growth,four types of polyethylene(PE)biofilm carriers and twelve tubular biofilm reactors with a diameter of 44 mm which were made of acrylic material were chosen.Each kind of the biofilm carrier was enclosed into three tubular biofilm reactors and lashed with flow velocity of 0.15 m/s,0.25 m/s,0.35 m/s,respectively,the biofilm carrier’s loading height was 40 mm,flow velocity was controlled by plastic flowmeters and the pipe connection used polyvinyl chloride(PVC)pipes and transparent plastic hose.In order to avoid suspended solids(TSS)in aquaculture wastewater having an impact on the experimental results,this study used artificial water,the concentration of NH₄-N was 2 mg/L,DO was 6-9 mg/L and pH was 7-8.At the same time,the flow pattern of Diversion Moving Bed Biofilm Reactor was simulated by Computational Fluid Dynamic software to observe the state of water flow at different aeration rates.After sixty days,the biofilm thickness of different types of biofilm carriers in different flow velocity were observed with electron microscope.The result showed that the biofilm thickness decreased with the increasing of flow velocity,the thickest biofilm with the thickness of 70 μm occurred at the lowest velocity of 0.15 m/s and the thinnest biofilm with the thickness of 20 μm occurred at the highest velocity of 0.35 m/s.There were no significant differences in biofilm thickness among different structures of biofilm carriers.When the simulation of aeration rate of reactor was set at 0.6 m/s,its integrated flow pattern and biofilm growth situation were the best,the flow velocity in downflow area was 0.06-0.12 m/s and in upflow area was 0.24-0.3 m/s,the eddy area accounted for 10%.The data indicated that the hydraulic condition rather than the structures of biofilm carriers with same material was related to biofilm growth,and low flow velocity is favorable for biofilm growth.Besides,the aeration intensity and reactor’s structure are important factors affecting the Diversion Moving Bed Biofilm Reactor’s flow pattern.This study provided basic data about design and operation for such reactors,and it could be very practical to use the method of combination of experiment and simulation to study biofilm growth and flow pattern,and the data and the method could also be applied to a variety of fields.