IsaMill (TM) is a high-speed stirred mill used in the mineral industry for a range of milling duties from ultra-fine to coarse grinding. In this work, numerical simulations based on the discrete element method (DEM) were performed to investigate the particle flow in a dry stirred mill with a similar configuration to that of an IsaMill (TM). The effects of operational variables such as mill loading and rotation speed on flow properties such as flow velocity, power draw, collision frequency, collision energy and total impact energy were analysed. The results showed that increasing mill loading or mill speed increases impact energy between particles. Moreover, physical experiments were conducted to quantify grinding performance under similar conditions. The experimental results showed that the grinding in the mill follows the first order kinetics, and the rate constant can be correlated to impact energy. The findings are useful to understand and optimise the particle flow and grinding behaviour of IsaMills (TM). The proposed methodology may also apply to other stirred mills.