Abstract: Numerical simulation was performed to study the internal mixing chamber flow field of a premixed abrasive water jet descaling nozzle by FLUENT software based on a CFD (computational fluid dynamics) multiphase flow mixture model. The effects of abrasive supply modes as well as different parameters under bilateral high-pressure water entrances such as abrasive and high-pressure water inlet diameters, high-pressure water inlet location and angle, and contraction cone angle on the flow field uniformity were analyzed to obtain reasonable structure parameters. Numerical calculation results show that the mixing uniformity of the internal mixing chamber for the abrasive entering by the central entrance mode is superior to that by the bilateral entrance mode at constant entrance velocity. The jet velocity out of the internal mixing chamber increases with the increasing abrasive and high-pressure water inlet diameters, but the outlet abrasive concentration increases firstly and then decreases as the high-pressure water inlet diameter increases. The location of bilateral high-pressure water entrances has relatively little effect on the mixing uniformity of the internal mixing chamber. When the mass flow ratio of abrasive to high-pressure water is about 3:4, and when the high-pressure water inlet angle and contraction cone angle are set at 30°, a relatively uniform flow field can be obtained.