Multiphase pump is widely applied for the exploitation of oil-gas resources in off-shore platforms. It is essential to investigate the performance of multiphase pumps when handling high viscosity fluid. A three-stage helico-axial multiphase pump with working fluids under various viscosities is investigated in the present study. Both energy performance and flow fields have been discussed with different viscos-ities. The influences of viscosity, flow rate and blade height on the distribution of turbulence kinetic energy are analyzed. Results show that both pump head and efficiency gradually reduce with the rise of viscosity when handling high viscosity fluid. The rise of viscosity and blade height, and the decline of flow rate will lead to an increase of turbulence kinetic energy. Characteristics of partial differential equations are employed to reveal the influence of viscosity, and a theoretical model has been established to predict the influence of flow rate. (c) 2020 Elsevier Ltd. All rights reserved.