Abstract: The application of ultrafine fogging and dustfall technology in underground tunnels greatly enhances dustfall efficiency. However, it may lead to reduced visibility in the roadway, creating safety risks. To solve this problem, by establishing the evaporation-dispersion model, the influence of particle size, environmental temperature, relative humidity, and wind velocity on the evaporation and dispersion characteristics of droplets was investigated. The results show that: with the decrease of the droplet particle size, the complete evaporation time is shortened, and the shortening rate is gradually increased. When the droplet size decreases from 200 μm to 20 μm, the complete evaporation time shortens from 7.350 0 s to 0.001 9 s, wihich means a reduction of 99.97%. Additionally, as environmental temperature increases and relative humidity decreases, droplet evaporation rates increase. When the temperature increases from 5 ℃ to 30 ℃, the complete evaporation time for droplets with a particle size of 20 μm was reduced by 80.0%. The rate of droplet evaporation decreases rapidly after the relative humidity reaches 80%. With the increase of wind speed, the distance of droplet dispersion was increased. Ultrafine droplets with a particle size of less than 20 μm were the main component of dispersed droplets. Fog droplet dispersion characteristics were measured in an underground coal tunnel. With the increase of roadway distance, the average particle size, volume concentration, and number concentration of fog droplets decreased gradually, and then decreased rapidly after reaching 45 m. Large particle size droplets settled gradually, and small particle size droplets dispersed in the roadway. The center of the roadway cross-section is the area where fog droplets accumulate, which is the key position that affects the visibility of roadway.