Abstract: In view of sand water conditions, fluid machinery acted on by a force of sand, in which impeller is the main work part is easy to erode and loses its original function. In order to study the influence of the particle size of sand in water on the erosion of screw centrifugal pump, N-S equation and standard k-ε turbulence model are used and the internal flow field of screw centrifugal pump is numerical simulated. The results show that the sediment is constant, the particle size has significant impact on the erosion of impeller, and the volume concentration gradient varies very uneven, which increases the erosion of the impeller, and promotes the erosion effect, the impeller flange wear is most serious.