Droplets generated in industrial buildings may do harm to the workers, the construction and the environment. Ventilation is often used to control this kind of air-borne contaminants. In order to provide a basis and reference for the efficient ventilation on droplets control, a numerical simulation method is adopted to reveal the evaporation and movement of fine water droplet populations released from a tank in industrial buildings. The variations of diameter and velocity of water droplets with identical initial diameter and velocity were studied. The results showed the evaporation and movement of the droplet populations presented obviously nonuniform distributions, due to vapor concentration and velocity distribution of the air around the droplets. When the droplets were closer to the centerline of the tank, they showed a lower evaporation rate, a larger velocity and a bigger velocity difference between droplets and its surrounding air. The effects of initial diameter and the relative humidity of the ambient air on droplet evaporation and movement were discussed. Compared to the relative humidity of the ambient air, the initial diameter had a more significant effect on the droplet evaporation and movement. The effects of the initial diameter variation (1 µm–50 µm) on the evaporation time variation and the terminal height variation were almost 17 times and 10 times larger than the effects by the relative humidity variation of the ambient air (20%–80%), respectively.