To address the optimization of flow field characteristics and crystallization quality in potassium salt crystallizers. Based on a CFD-PBM coupled model and combined with the crystallization kinetics of KCl, the effects of stirring speed, double-layer impeller structure, and crystallizer geometry on the two-phase flow field and crystallization process of a DTB-type potassium salt crystallizer were systematically investigated. The strength of the double-layer impeller was verified through fluid-structure interaction analysis. A stable flow field circulation was formed and particle uniformity was improved at 45-75 rpm. Excessive speed, however, inhibited the growth of large particles and increased the proportion of fine crystals due to enhanced shear. The optimal structural parameters were a crystallizer top-to-bottom ratio of 2.3 and a guide tube height-to-diameter ratio of 1.6. The impeller speed is the main factor affecting particle suspension and particle size distribution (CSD). The double-layer impeller structure significantly improves the mixing effect. The optimized structure can significantly reduce energy consumption, while meeting the strength and stiffness requirements. This provides a theoretical basis for the design optimization and industrial application of potassium salt crystallizers.