Considering the characteristics of complex structures in the oxidation ditch with eccentricity diversion wall,a numerical simulation was carried out for the water flows by using CFD program FLUENT. The radial eccentricity along the diversion wall from 0~1.0m and 0.25m interval for changes in the location of the eccentricity, the velocity of the flow field in the oxidation ditch are computed and analyzed. The results show that the eccentricity of the diversion wall will improve on the low water flow areas behind wall and eliminate sludge deposition. With the increase in the eccentric value diversion, the second low-velocity flow area behind radial wall will be formed. Comparing different the velocity curve of eccentricity in the oxidation ditch, the eccentricity of the diversion wall should be set up between the 0.3m~0.4m. This study provided theoretical basis for the diversion wall design.