Abstract: This paper reports full-passage numerical simulations of a high-head Francis turbine using a solid-liquid two-phase flow model to preliminarily study the influence of particle diameters and concentration of sediment on the internal flow and performance of the turbine runner. The effects on sediment concentration distribution and mean pressure on the runner blades as well as on turbine efficiency were examined using a single variable method. Results show that relative to the flow of clean water, sediment in the flow causes an increase in pressure load on the blades and a decrease in turbine efficiency to a certain extent. Under the same operating conditions, higher sediment concentration appears around the inflow and outflow edges of the blade and near its joint with bottom outlet ring. When its particle diameters increase, sediment tends to be more concentrated and hence its abrasion is intensified.