The paper used Euler-Euler multi-fluid model and standard turbulence model to simulate the mechanical property of gas-liquid mixture in an aeration tank. The coupling solution of velocity and pressure used Phase-Coupled-SIMPLE algorithm.The following results are that the comparison results of simulated vertical velocity and the experimental data along the line z=0.71m in the center section(y=0.025m) are in good agreement.the inlet gas velocity has less impact on the vertical speed of upper mixture fluid in the aeration tank when the uperficial gas velocity is smaller.But when the superficial gas velocity is larger,the middle section of the whole aeration tank shows the law that the vertical velocity close to the center is great, and that close to both side walls is small and negative values.The rising bubbles can easily appear swing due to wall attachment effect, and the greater the superficial gas velocity, the more obvious is the wall attachment effect. The analysis result of mechanical properties in the aeration tank at different gas velocities can provide some reference value for the design and operation of aeration tank.