Evaluation of process parameters and performance of planetary mills is considered an important issue in optimization of their predicted efficiencies. The current research deals with a computer simulation based on discrete element method (DEM) employed to evaluate the grinding mechanism of a planetary mill. The effect of rotational speed, the volume percentage of the balls and powders on impact energy, the frequency of the impacts, the abrasion of the balls and the dissipated energy have been investigated. It was realized that by increasing the rotational speed, the impact energy and the number of impacts of ball-ball, ball-container, ball-powder, powder-powder and dissipated energy were increased. By increasing the balls filling ratio, the impact energy value of ball-ball remained almost constant after a critical point while those of ball-powder impact energy and the dissipated energy were slightly increased. With an increase in powders filing ratio, a maximum value was observed for the ball-powder impact energy; however, the ball-ball impact energy remained almost constant and the dissipated energy indicates a reduction in rate. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.