The work aims to provide suggestions for expanding service life of servo spool valve by studying characteristics and law of contaminant wear to servo spool valve by particle impurities. By combining computational fluid mechanics (CFD) with erosion theory, the erosion model of servo spool valve flow field was built to simulate the erosion wear of servo spool valve. Sharp-edge of valve port‘s controll surface was seriously damaged by erosion wear, and wear rate of the sharp-edge of groove was clearly higher than that of the sharp-edge of shoulder. The relation between the wear rate of valve port and the particle concentration was linear and positively correlated, yet both the wear rates of the sharp-edges of groove and shoulder reduced as the opening of valve port increased. When the mass flow rate was constant, the erosion rate of valve port increased as a whole as the diameter increased. The valve port was more sensitive to one particle of certain diameter. As the opening of valve port increased, the diameter of particle to which the valve port was sensitive increased as well. In order to improve the wear resistance, the valve port shall be reprocessed by fabrication processing. To a certain extent, the erosion rate declines if the spool valve works at big opening. The wear caused by particles of large diameter is severer and should be controlled strictly during oil purification.