Abstract: The dust removal efficiency of spray dust removal technology is closely related to the wettability of coal dust, which is affected by many factors. In order to study the influence of particle size on the wettability of coal dust, four kinds of coal fines with different particle sizes in Yannan Coal Mine of Inner Mongolia were taken as the research object, and the influence law of particle sizes on wettability of coal dust were discussed from four aspects including contact angle, settling efficiency, infrared spectrum and heat of wetting. The results show that when the particle size increases gradually, the contact angle decreases gradually, and the hydrophilic sedimentation effect is significant; the change of particle size does not cause the loss of functional groups of coal dust, but with the decrease of particle size, the oxygen-containing functional groups decrease, and the hydrophilic influence factor of coal dust decrease; the heat of wetting has a negative correlation with the particle size of the same kind of coal dust and a positive correlation with the contact angle, therefore, heat of wetting can be used to represent the wettability of coal dust of different particle sizes. The research results can provide some references for improving the wettability efficiency of coal dust and the development of coal dust control technology.