Abstract: Slurry pumps are widely used in the transportation and treatment of various solid-liquid mixtures. At present, research on slurry pumps is mostly based on single particle solid-liquid two-phase flow research, and the particle size is small. However, the actual solid-liquid two-phase flow transported by slurry pumps during operation is a multi-scale mixed particle. In order to reveal the multi-scale particle motion characteristics inside the slurry pump, a visualization test system for the internal flow of the slurry pump was built. The visualization of the multi-scale particle solid-liquid two-phase flow under rated conditions was captured, and the effects of impeller rotation, particle concentration, particle density, and particle size on the particle distribution and mixed transport characteristics inside the pump were studied. The experimental results show that the volume concentration of particles from the 5th to 9th sections of the volute and near the outlet of the volute is higher with the impeller rotates. As the particle concentration increases, significant particle accumulation occurs from the 5th to 9th sections of the volute, and the concentration also increases from the 2nd to 4th sections of the volute. When mixing particles with similar sizes, the particle distribution inside the pump is determined by the particle density. When mixing particles with similar density, the particle distribution inside the pump is mainly determined by the smaller particles.