Physical model of pre-mixed abrasive water jet nozzle is established. Based on the software of FLUENT, numerical simulation of wear characteristic of abrasive water jet nozzle was carried out by use of particle trajectory model, Grant collision elastic recovery coefficients and E/CRC erosion model. The simulation results show that there are two severe wear sections for nozzle wear, locating within a short distance range before the entrance of cylindrical section of nozzle and before the exit of cylindrical section of nozzle respectively, when the contract angle of nozzle is above 20°. The collision frequency and velocity of abrasive particle with the wall of cylindrical section of nozzle increase with the increase of contract angle of nozzle. At the same time, wear rate of the wall of cylindrical section of nozzle increases integrally and the range of severe wear section expands with the increase of the ratio of cylindrical section length to exit diameter of nozzle. These cause the wear of cylindrical section of nozzle aggravating. The overall wear degree of the nozzle is characterized by the areaweighted average integral of nozzle wall wear rate. The area-weighted average integral of nozzle wall wear rate increases, namely the overall wear degree of the nozzle is more serious with the increase of contract angle and the ratio of length to diameter of nozzle. Therefore, the contract angle and the ratio of cylindrical section length to exit diameter of nozzle is selected small for better from the point of view of reducing the wear of the nozzle.