Research on the numerical simulation of gas-liquid mixing flow under the influence of radius in a stirred tank could provide references for the design of stirred tanks. The RNG k-ε turbulence model as well as multiple reference frame method was used to simulate the mixing process of gas and liquid in the single impeller stirred tank to obtain the mixing of two phases of actual flow in a stirred tank with the same ventilation rate and rotational speed, and different radiuses. The influences of different impeller's radiuses on the distribution regularities of velocity magnitude and gas holdup in different sections were analyzed. The results of simulation showed that the changing in radius almost caused no effects on the air volume fraction, while the velocity distribution was affected to a certain extent.