The flows of water as well as viscous oil in the three rectangular sections of the volute of a centrifugal pump are measured by using a two-dimensional laser Doppler velocimetry(LDV) in the best efficiency and part-loading points, respectively. The results show that the magnitude of tangential component of absolute velocity is one order larger than that of radial component. There are spiral motions in the sections of the volute. The angular momentum of liquid in the volute isn’t conservative and the viscosity of liquid is larger, this situation is more severe. The flow of water or viscous oil in the volute is diffused in both best efficiency point and part-loading points. The diffusion of the flow is weakened while pumping the viscous oil. The flows of water as well as viscous oil in the three rectangular sections of the volute of a centrifugal pump are measured by using a two-dimensional laser Doppler velocimetry (LDV) in the best efficiency and part-loading points, respectively. The results show that the magnitude of tangential component of absolute velocity is one order larger than that of radial component. There are spiral motions in the sections of the volute. The angular momentum of liquid in the volute is not conservative and the viscosity of liquid is larger, The flow of water or viscous oil in the volute is diffused in both best efficiency point and part-loading points. The diffusion of the flow is weakened while pumping the viscous oil.