<p>Rock particle size distribution (PSD) during ball milling is heavily influenced by mechanical parameters like Vickers hardness (HV) and brittleness (B). This study analyzes nine rocks with different lithologies, first using multifractal theory to examine the effects of hardness and brittleness on PSD. The results show that the range, uniformity, and concentration of the PSD follow distinct patterns with varying hardness and brittleness. The brittleness index has the greatest impact on the range and concentration of PSD, followed by hardness, while uniformity is similarly influenced by both hardness and brittleness. Furthermore, the heterogeneity of PSD increases with hardness, showing fluctuations, decline, and subsequent increase. With brittleness, it exhibits fluctuations, decline followed by increase, and final decline. As hardness and brittleness increase, the PSD variation shifts from larger to both large and small particles. Finally, the joint multifractal approach quantifies the impact of hardness and brittleness on PSD, revealing the relationship between rock properties and particle size distribution.</p>