Abstract: Acoustic collision-coalescence is a technique that utilizes a strong acoustic field to continuously promote collision and merging among micro liquid droplets,and it has gradually gained attention in research areas such as defogging and cloud seeding in recent years.This paper reviews and analyzes the impact mechanism of acoustic waves on the coalescence process of micro liquid droplets.By comparing and analyzing turbulent coalescence in natural precipitation with factors such as acoustic-induced coalescence and the acoustic wake effect,the paper introduces a parameter—acoustic action ratio—to quantify the relative effects of acoustic waves.Based on this,the optimal frequency range for acoustic rainfall enhancement is determined,and the differences in the relative effects of acoustic waves under different cloud conditions are analyzed.The results indicate that the optimal frequency for a typical droplet pair of 10~20μm is 65Hz,and the optimal frequency range is defined as 33Hz to 128Hz,where the effects on both sides are approximately equal.In practical field cloud seeding projects,the acoustic action ratio at a frequency of 125Hz under layered cloud conditions at an altitude of 5km is 4.36,indicating a noticeable increase in coalescence effects.However,under heavy rain conditions,the acoustic action ratio is much lower than under layered cloud conditions.The findings can provide practical guidance for the implementation of field cloud seeding projects.