Abstract: In the low-pressure abrasive air jetting, as a novel assisted rock-breaking technology, supersonic abrasive ejection is achieved at 2 MPa through a rectangular cross-section nozzle to improve efficiency. The stability and efficiency of the jet are affected by the impact and wear caused by the abrasive colliding with the inner wall of the nozzle. To clarify the influence of structural parameters on the wear characteristics of nozzles in low-pressure abrasive air jetting, nozzle wear behavior was investigated by numerical simulation of fluid flow in nozzles using a coupled CFD-DEM method integrated with the Archard wear model. The impact of converging section length, throat size, and diverging section length on nozzle wear was examined. A second-order response surface model was established to quantify the significance of the effects of structural parameters on nozzle wear by the Box–Behnken experimental design method. An optimized nozzle structural design was proposed. The results show that the wear of the rectangular nozzle is primarily concentrated on the rear part of the convergence section and the front part of the expansion section, with the wear area in the expansion section exhibiting a U-shaped distribution. A negative correlation was observed between the length of the converging section and the maximum wear depth of the nozzle. When the length of the convergence section increases from 10 mm to 30 mm, the wear depth decreases from 1.25×10⁻⁵ mm to 2.82×10⁻⁶ mm, a decrease of 77.4%. A negative correlation was also identified between the maximum wear depth of the nozzle and the throat size, whereas the maximum particle ejection velocity was affected by the throat size, exhibiting an initial increase followed by a decrease. The maximum wear depth of the nozzle was influenced by the length of the diverging section, showing an initial increase followed by a gradual decrease, while the maximum particle ejection velocity was increased under the influence of the diverging section length. The optimized nozzle parameters are 30 mm for the convergence section, 3.12×10.38 mm² for the throat and 157 mm for the expansion section, which is 68.87% lower than the standard nozzle wear depth and 5.83% higher than the maximum speed of abrasive particle ejection, achieving a balance between low wear and high efficiency. This study provides theoretical support for improving the life of Laval rectangular section nozzles.