The 3D flow field generated by two-stage impellers in the agitation of xanthan gum, a pseudoplastic fluid with yield stress, was simulated using the commerical CFD package. The effect of impeller speed and impeller spacing on power number, cavern size and viscosity distribution was investigated in this work. The results showed that the power number was slightly influenced by impeller spacing. Higher impeller speed and larger impeller spacing contributed to creation of a bigger cavern. The range of high viscosity zone between the impellers increased with an increase in impeller spacing. Impeller speed and impeller spacing could be used as important parameters to improve the mixing performance of multi-stage impellers in the mixing of pseudoplastic fluids with yield stress.