In order to break through the bottleneck in the development for the oil-coal-water slurry to serve as the alternative fuels, this paper studies the problem of substituting the oil-coal-water slurry for the diesel fuel to be used on diesel engines where solid coal particles would exacerbate the piston pump wear, and carries out a multi-phase numerical simulation to identify the media-induced piston wear mechanism. Based on the VOF multi-medium model, the Reynolds stress model and the discrete phase model for the continuous phase and the dispersed phase, the multi-medium erosion, the motion trajectory of the solid particle and the impact process between the solid particle and the machine surface are simulated. The volume content of the solid phase in the multi-medium flow is lower than 10% in this simulation model. The simulation result shows that, the related parameters of the solid particles, such as the density and the diameter, the mix proportion and the plunger speed of the impeller, would greatly influence the motion trajectory and the impaction of the solid particles with the machine surface. The solid particles with a large mass are apt to move toward the working surface and impact the inside of the piston shell. On the other hand, the small particles are liable to impact the plunger barrel assembly. The higher the plunger speed, the more plunger barrel assembly erosion will be resulted; the plunger barrel assembly wears more severely with the increase of the solid mix proportion. Simulation results agree with experimental results.