Abstract: Abstract: Biofloc technology (BFT) has been widely used in situ tilapia rearing for its benefits such as saving protein-feed and reducing the adverse impacts on environment. And biofloc concentration has huge effect on aquaculture system. More specifically, TSS(total suspend solid) and the uniformity of the biofloc distribution can greatly affect cultured animals on feeding enthusiasm, and high TSS even will threat the survival of breeding objects. In production, because of the biofloc sedimentation, the bottom of traditional BFT system usually extremely high, so the recirculating biofloc technology (RBFT) system has become a hot topic in recent study. To investigate the improvement on biofloc distribution uniformity of RBFT system compared with situ BFT system, an Euler-Euler multi-phase turbulence 3-D model combined with the kinetic theory of granular flow was applied to simulate the solid-liquid-gas three-phase flow in culture ponds of two kinds of BFT system. At first, the tank meshing was finished based on the commercial software Workbenching 15.0. The grid independent validation was done to choose the acceptable mesh. At last, the mesh was imported in numerical simulation software (Fluent) to analyze the velocity contours and streamlines of liquid phase, distribution characters of solid phase in these two models. In this simulation, pressure-based solver and second-order implicit transient formulation were adopted. The boundary conditions of water and air inlet were set as velocity, and their outlet were regard as pressure outlet equated to the local atmospheric pressure. What's more, according to the SIM-PLE algorithm, pressure-velocity coupling was calculated. The bioflocs were regarded as to be distributed in the bottom initially. Unsteady simulations were performed when all residuals fall below 10-3, while 40 iterations per time step were used to ensure numerical stability. To have an accurate results, third-order monotone upstream-centered schemes for conservation laws (MUSCL) was used. The simulation results show that when the hydraulic retention time (HRT) of RBFT system is 0.45 h, its flow field has an irregularly varying flow directions namely spreading all over the space, and a severe turbulent flow is complex in contrast with BFT system. On one hand, this flow field results in a more homogeneous velocity distribution and less dead zone flow field in recirculating culture pond, and on the other hand, bioflocs are gathering at the main center area, which is beneficial to biofloc recirculating. What is particularly worth mentioning is that there is only a small amount of biofloc's sedimentation at bottom in recirculating culture pond, and this result can efficiently avoid the anaerobic bacterium's breeding caused by the biofloc sedimentation at bottom corners of culture ponds. In addition, the solid phase volume fraction is about 0.1 in recirculating culture pond's model, and this concentration of suspended solid is suitable for growth of cultured aquatic animal like tilapia and shrimp. According to the comparison between simulation value and experimental data, the simulating value's error is less than 20%, and the simulation results are trustworthy. In conclusion, the study shows that the RBFT system can overcome the disadvantages including uneven distribution of biofloc and too much dead zone in situ BFT system.