This study investigates the effect of ultrasound on the evaporation and crystallization of sessile NaCl solution droplets in both traveling and standing wave ultrasound fields. The results show that ultrasound significantly accelerates droplet evaporation and refines crystal grains. In traveling wave ultrasound fields, the evaporation time and appearance time of NaCl grains increase with the distance between the droplet and the ultrasound emitter, while in standing wave fields, the evaporation rate increases with the distance. Overall, traveling wave ultrasound fields have a stronger effect on grain refinement than standing wave fields. Grain refinement is attributed to the reduction of the critical nucleation radius due to ultrasound energy and the increased nucleation rate from accelerated evaporation. Additionally, ultrasonic cavitation-induced grain breakage contributes to grain refinement. The study also reveals that the acoustic streaming in ultrasound fields enhances heat and mass transfer, promoting faster evaporation and nucleation. In traveling wave fields, the acoustic streaming creates different flow patterns that influence the distribution of NaCl crystals. In standing wave fields, the acoustic streaming induces unidirectional circulation, leading to crystal accumulation at specific positions. The grain size in traveling wave fields is significantly smaller than in natural evaporation, with the smallest grains observed at positions where the acoustic pressure is highest. The study provides insights into the mechanisms of ultrasound-induced grain refinement and offers a reference for controlling evaporation rates and grain refinement in saline droplets.This study investigates the effect of ultrasound on the evaporation and crystallization of sessile NaCl solution droplets in both traveling and standing wave ultrasound fields. The results show that ultrasound significantly accelerates droplet evaporation and refines crystal grains. In traveling wave ultrasound fields, the evaporation time and appearance time of NaCl grains increase with the distance between the droplet and the ultrasound emitter, while in standing wave fields, the evaporation rate increases with the distance. Overall, traveling wave ultrasound fields have a stronger effect on grain refinement than standing wave fields. Grain refinement is attributed to the reduction of the critical nucleation radius due to ultrasound energy and the increased nucleation rate from accelerated evaporation. Additionally, ultrasonic cavitation-induced grain breakage contributes to grain refinement. The study also reveals that the acoustic streaming in ultrasound fields enhances heat and mass transfer, promoting faster evaporation and nucleation. In traveling wave fields, the acoustic streaming creates different flow patterns that influence the distribution of NaCl crystals. In standing wave fields, the acoustic streaming induces unidirectional circulation, leading to crystal accumulation at specific positions. The grain size in traveling wave fields is significantly smaller than in natural evaporation, with the smallest grains observed at positions where the acoustic pressure is highest. The study provides insights into the mechanisms of ultrasound-induced grain refinement and offers a reference for controlling evaporation rates and grain refinement in saline droplets.