Aiming at the problem of high energy consumption and sludge deposition that could occur in oxidation ditch sewage treatment technology, the viscosity and settling rate of activated sludge was imported into Fluent software through a user-defined function, and then the numerical simulation for water-activated sludge two-phase flow calculation of standard oxidation ditch in a sewage treatment plant was conducted. The power of thruster, the distribution of velocity and sludge in the oxidation ditch could be obtained. Compared with each other, the optimal motor power and velocity distribution was selected. The flow field characteristics of the oxidation ditch were further analyzed and compared the section flow velocity obtained by numerical simulation with the experiment measurements, showing that the data from the measuring points has good performance of consistency, and the velocity of each point in the real flow field can be well predicted by numerical simulation. The sludge mass concentration is generally higher in the area with high velocity dead zone rate.