Abstract: Coal water slurry (CWS) requires a certain fineness and size distribution of the coal powder to obtain higher packing density. In practice, grinding methods exert an important influence on these parameters. In this study, a ball mill, a rod mill and a planetary mill were used to grind a long flame coal. The particle size distributions and their packing densities with different grinding methods at different grinding time were tested and analyzed through fitting the data by Rosin-Rammler model. The results showed that the grinding efficiency of the ball mill and the planetary mill were much higher than that of the rod mill. Their products were much finer. However, the size distributions were narrower, and their packing densities were much lower than that of the rod mill. The uniformity index of the Rosin-Rammler equation had a well linear relation with the packing density when its values varying 0.75~1.3. Therefore, the uniformity index could be used as a fast evaluation method for the particles packing density.