Abstract Liquid desiccant dehumidification system has received much attention in recent years for its important economic benefits in energy saving of buildings. Furthermore, the specific surface area of desiccant solution can be expanded dramatically by the ultrasonic atomization technology, which generates numerous tiny droplets with diameter about 50 μm. However, the tiny atomized droplets are found to be easily captured by the wall of dehumidifier chamber, resulting in the poor performance of this type of system. In this paper, a new criterion called “droplets suspension rate” together with an optimized design method was proposed to improve the performance of ultrasonic atomization liquid desiccant dehumidification system via optimizing its dehumidifier chamber. Experiments were carried out to verify the improvement, where the dehumidification effectiveness, desiccant consumption rate and the air temperature rise were adopted as indicators to evaluate the performance of the system. The results showed that the performance of ultrasonic atomization liquid desiccant dehumidification system was enhanced significantly and the desiccant consumption was reduced markedly after the improvement. Moreover, the improved system was found to be able to utilize lower-grade desiccant solution. The criterion and the method proposed may build a foundation for the better design of ultrasonic atomization liquid desiccant dehumidification system.