Abstract: The magnetic flow follower method was used to measure liquid circulation time distribution (CTD) in a stirred bioreactor. CTD was studied in water and CMC solution systems with Rushton turbine and two kinds of axial flow impeller respectively. The mixing performance of the three impellers was evaluated. A structured mixing model was developed for agitated bioreactor with a single impeller. The model parameters were evaluated by fittng the model prediction results with the experiment data of the flow follower method. The parameters under different experimental conditions were investigated and compared. The results showed that the axial impeller had better mixing performance than Rushton turbine for non -Newtonian, high viscous fermentation processes.