With the purpose of solving the problems of uneven velocity and energy dissipation of the foreign fiber sorter, this paper has analyzed and designed the nozzle arrangement and structure in the foreign fiber rejection system. According to the effect of the wall surface distance, the turbulence kinetic energy was optimized through a circular arrangement of nozzles. the nozzle was optimized with the contraction-expansion structure based on the relationship between the Mach number and the nozzle’s cross-sectional area. The stepped cross-section of the nozzle was replaced by an transition curve cross-section and different cross-sections were designed by using methods, such as the Witosynski method and the Foelsch method. Through calculation and simulation for the nozzles before and after optimization, based on the velocity, pressure and turbulence kinetic energy nephograms, the optimized outlet velocity of the nozzle was more uniform to demonstrate the rationality and effectiveness of the proposed method.