This study investigates the grinding performance of Fluid Energy Mill (FEM) through experimental studying and numerical simulation. The experimental parametric study shows that the mean product particle size decreases with grinding pressure (GP) and increases with the solid feed rate (SFR). In comparison, the influence of the feed pressure (FP) on the product size is much less significant. Visualization study indicates the existence of a particle-concentrated layer near the peripheral wall region, named the grinding region in this article since most of the collision-induced size reduction occurred in this region. The grinding air streams re-orient the particles, facilitating particle-particle and particle-wall collisions downstream in the grinding region. To understand the influence of the particle-wall collision, the peripheral wall of FEM was coated with a foam film in some experiments. The particle-wall collision was found to play a significant role in size reduction, especially under low air pressure. The gas flow inside the grinding chamber was simulated as the initial step to the ongoing 2-phase flow simulation of the milling process in the FEM. The simulation results show that eddies are formed at the feed air entrance, which explains the tendency of fine particle deposition in this region. The simulation results also suggest a strong relationship between the GP and the mean gas velocity in the grinding region. (C) 2009 Elsevier B.V. All rights reserved.