The gas holdup in an air?water systems is measured using the method of differential pressure and the electric conductive probes. N and M are measured by the torque transducer and used to calculate the power input. A physical model was developed to predict the total gas holdup in a gas?liquid stirred vessel by dividing the gas in the liquid into two parts that A is the one entering and quitting the liquid, and B is the other recycling in the liquid, respectively, The results indicate that based on the difference between flow regimes in gas?liquid systems, it is reasonable that the total gas holdup should divided into two stages: ?total??Vs? for the flooding condition, ?total??Vs?+?PV?Vs? for the loading/completely dispersing conditions, and as for DT+DT, ??6, ??1, ??0.32, ??0.56, ??1. The results from literatures are predicted by the model reasonably. The model is reasoned for some other types of dual-impellers, in which ? is controlled by the types of the impellers.