The operational efficiency and stability of pump-turbines under sediment-laden flow conditions are critical concerns in hydraulic engineering. A prototype pump-turbine used in a pumped storage power station was numerically investigated to evaluate energy losses under wide load conditions (50%P_r~ 100%P_r,where P_r is precision of convergence). Based on entropy production theory and the SST k-ω turbulence model, the internal sediment-water flow was simulated, and the energy loss characteristics under different operating loads were analyzed. Results indicate that energy losses primarily consist of indirect entropy production and wall-induced entropy production. As the load decreases, indirect entropy production significantly increases, reaching 2.1 times that at 100%P_r, under the 50%P_r condition, while wall-induced entropy production gradually decreases. The runner and draft tube are identified as the main contributors to energy loss. The proportion of entropy production in the runner rises with decreasing load, exceeding 50% at 50%P_r. Vortex structures are mainly concentrated in the flow passage between the pressure side of long blades and the suction side of short blades. Load variations affect vortex structure and velocity gradients, thereby influencing turbulent pulsations and near-wall velocities, leading to spatial variations in energy dissipation. Wall entropy production is primarily concentrated near the high-pressure side of blades and the low-pressure side adjacent to the band. These findings provide theoretical support for energy loss assessment and operational optimization of pump-turbines under sediment-laden conditions.