Dust particles floating inside roadways are characterized by various sizes. However, it is difficult to replicate the dust environment with such factors taken into consideration in laboratory experiments. Fortunately, computational technology provides an alternative way for that. In this study, in order to investigate the movement mechanism of dust with different diameters from heading face in the underground roadway, a three-dimensional CFD-DEM coupling numerical model is presented using the Eulerian-Lagrangian method. A numerical roadway model based on a practical engineering case has been established for the purpose of studying the dust diffusion under single-forced ventilation condition in roadway underground. The study suggests that particle size has a significant effect on dust dispersion. The results demonstrate that CFD-DEM coupling computational simulation can be an effective approach for the investigation of dust issues in underground engineering.