Mixing behavior of particles is an essential process for a ball mill. In order to investigate particle mixing, a three dimensional model was established for particle dynamics in a ball mill. Firstly, the Discrete Element Model was adopted to track each particle in the ball mill. Meanwhile, different kinds of collisions, the relative friction for particle movement, and other conventional forces were considered. Then, the bulk movement of particles in the ball mill was explored based on the established model. In addition, the detailed characteristics of particle mixing dynamics in the ball mill were studied with multiple methods, including visual observation, collision detection, and mixing extent. It was found that the contact number of target particles increased fast in the beginning, then collapsed to one unique value when particle mixing became uniform, which finally fluctuated around the unique value periodically with the mill rotation. Moreover, multiple effects of particle size, particle density, uneven granularity and rotational velocity on particle mixing were discussed for particle mixing dynamics. In addition, selected mixing curves were present to provide more mixing information of particles in different areas of the mill. Furthermore, Boltzmann model was found to be available for mixing dynamics with the defined contact number. Additionally, selected stimulation results were compared with relative previous experimental results, and reasonable agreements could be obtained. The present work could provide consults for collision dynamics and mixing behavior of particles in ball mills. (C) 2016 Elsevier B.V. All rights reserved.