Abstract: The ultra-low head bulb tubular turbine units have great potential in both the capacity-increasing of power plants and ultra-low head development. However, the sediment carried in the flow will have a negative impact on the operation of units, especially in the flood season. The study of sediment erosion is of great significance to the stable operation of units. Based on CFX code, k-ε turbulence model, Lagrangian particle tracking model, and Tabakoff and Grant erosion model were used to calculate the solid-liquid two-phase flow of two-blade bulb tubular turbine under 2.1m ultra-low head. In this paper, the reliability of numerical simulation was verified by experiments. The swirl characteristics under single-phase and two-phase flow conditions were compared. The influences of different sediment concentrations and sizes on the erosion location, erosion rate, and flow characteristics of flow passage components were explored. The conclusions are as follows: Compared with the vortex in clear water, the vortex in sediment-laden flow is enhanced. The concave surface of the guide vane, the head of blades inlet edge, the blade outlet edge, the runner rim, and the runner chamber are more vulnerable to sediment erosion. With the increase of silt particle concentration and size, the erosion area, erosion degree, and maximum erosion rate of guide vanes, blades, and runner chamber will also be increased. Compared with guide vanes, the hydro-abrasive erosion of blades and runner chamber is more serious. More attention should be paid to erosion protection during the operation in flood season.