Abstract: Crops in greenhouses can usually suffer from heat stress under high temperatures, resulting in slow growth and even death. The temperature inside greenhouses can rise to 40℃ to 45℃ in summer, particularly in the tropical and subtropical climate in South China. Therefore, ventilation and cooling are often required to maintain the temperature inside the greenhouse suitable for the crop growth. Among them, spray cooling has been commonly used as the prevalent evaporation. The tiny droplets can be sprayed to take away the heat in the environment via the latent heat of water evaporation. Once the incomplete evaporation occurs, the spray droplets can adhere to the plant surfaces, thereby promoting the occurrence of plant diseases and pests. In this study, a measurement platform for the suspended droplet evaporation was developed using the quadratic regression orthogonal rotation combination. A systematic investigation was also made to clarify the effects of the varying temperature, relative humidity, and velocity on the droplet mass transfer coefficient. A second-order prediction model was established for the droplet mass transfer coefficient. The dynamic variation was then elucidated during evaporation. The experimental results indicated that high accuracy was achieved in the second-order prediction model of the droplet mass transfer coefficient, with a coefficient of determination of 0.9427 and a corrected coefficient of determination of 0.9258. The variance analysis showed that the proportions of the temperature, relative humidity, and wind speed on the droplet mass transfer coefficient were 3.1%, 87.2% and 9.7%, respectively. A series of experiments was carried out to verify the model. The maximum error between the theoretical and the experimental value was 4.83%, the minimum error was 3.96%, and the average relative error was 4.42%. The experimental values were basically consistent with the predicted ones. The evaporation rate of droplets was then predicted under different environmental parameters. According to the single-factor and response surface analysis, the droplet mass transfer coefficient increased first and then decreased with the increase of the temperature and wind speed. There was a monotonic decrease with the increase in relative humidity. The maximum droplet mass transfer coefficient was obtained when the environmental temperature was 40℃, the relative humidity was 60%, and the wind speed was 2.4m/s. There was great variation in the dynamic mass transfer coefficient of the droplets during evaporation under different environmental parameters. The maximum mass transfer coefficient was 1.825g/m2/s, and the minimum was 0.130g/m2/s. There was a difference in the mass transfer rates of the droplets with the different volumes. The smaller the volume was, the larger the mass transfer coefficient was. The droplet mass transfer coefficient was obtained to determine the environmental parameters of the evaporation. The priority of the parameter regulation was ranked in descending order of the relative humidity > velocity > temperature. Therefore, the intermittent spraying and dehumidification can be expected to reduce the relative humidity inside the facility, thereby lowering the internal temperature for crops, particularly in the facility environment with high temperature and high humidity in South China. The precise control strategies of the spray cooling can further be explored on the mass transfer of the droplets under complex airflow fields and the interaction of multiple droplets in the future.