A newly designed two-grade fractal model for improving the packing state in brown coal water slurry (BCWS), which was built on the fractal theory and modified by separating the size into two grades, was investigated systematically. Packing efficiency (PE) and regression levels of the fractal model in various particle systems were analyzed. The results showed that the PE of brown coal particle system is determined mainly by the fractal characteristics of particles under 74 mu m and the packing state in BCWS can be significantly improved when the fractal dimension is around 2.6-2.7. In addition, the two-grade fractal model fits the PSDs for various particle systems with different graduation ratios of coarse samples (CS), fine samples (FS) and ultra-fine samples (UFS) well. PE reaches the maximum value when the graduation ratio is 7: 0: 3 (CS: FS: UFS) and the fractal dimension is 2.7080, which is consistent with the calculated results. It was confirmed by the slurry preparation experiment that the maximum solid loading of BCWS increased by 2.9% through optimizing the packing state using two-grade fractal model. (C) 2015 Elsevier Ltd. All rights reserved.