As the construction displacement and sand amount of overlong horizontal well are increased continuously,the erosion wear of ball seat of pitching sliding sleeve is increasingly serious.There are many researches on the erosion wear of liquidsolid twophase flow,but the influence of solid particles with mixed particle sizes to the erosion wear is not considered at all.The erosion wear of ball seat by the proppant mixed with different particle sizes was studied.Based on the Euler twofluid theory,the numerical simulation of the erosion wear of ball seat by mixed particle sizes was carried out with Fluent software.The results show that the erosion wear rule of ball seat is different caused by the solid particles with mixed particle sizes and the solid particles with single particle size.The erosion wear rate of ball seat by solid particles with single particle size is in inversely proportional to the particle size,while the erosion wear rate of ball seat by the solid particles with mixed particle sizes is related to the particle size and the volume ratio of the solid particles with different particle sizes.With the increasing of the volume ratio of the solid particles with small particle sizes,the erosion wear rate of ball seat presents a trend of decreasing first, and then increasing.The simulated result provides a reference for the selection of staged fracturing material of horizontal well.