Spraying is a main technique means for the prevention and control of coal dust in coal mines. The dust suppression efficiency by spraying is highly correlated with the wettability of coal dust. There are many influencing factors for the wettability of coal dust, among which the particle diameter of dust is one of the most significant factors. In order to analyze the influence of particle diameter on the wettability of coal dusts and the dust suppression efficiency via spraying, 18 different samples with 3 different types of coal samples and 6 different particle diameters were selected in this study. A series of experiments were designed and performed to evaluate the micro-properties, the wettability, and the dust suppression performance via spraying of coal dust. According to experimental results on the micro-properties, the amount of hydrophilic oxygen-containing functional groups gradually dropped with the decrease of the particle diameter. As the particle diameter decreased, the specific surface area of coal dust gradually increased while the average diameter of the internal pores decreased. Based on the experimental results on the wettability of coal dust, the wettability of the dust with the same property dropped with the decrease of particle diameter. Finally, based on the experimental results on the dust suppression efficiency via spraying, the dust suppression efficiency via spraying was determined by both the wettability of coal dusts and the value of AD 50 (the absolute value of the difference between the droplet diameter and the dust particle diameter). As the particle diameter of coal dust increased, the dust suppression efficiency via spraying first increased and then decreased. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.