Slurry transport is a very important means of transporting solids through a pipeline. To improve the efficiency of slurry transport, especially in coarse particle transport, which is subject to problems such as strong resistance and easy blockage, more of the internal structure of the flow must be known. Empirical and analytical models are inadequate for this purpose. Therefore, in this study, a coupling mechanism is established between the computational fluid dynamics (CFD) and discrete element method (DEM). The CFD-DEM coupling was applied and research was conducted on the internal flow structure characteristics of microscopic motion and flow transition for coarse particles in a pipeline. The flow-regime transition processes of coarse 10-mm particles were analyzed qualitatively at velocities of 2 m . s(-1), 5 m . s(-1), 8 m . s(-1) and 10 m . s(-1) in a 0.1524-m diameter pipe, and quantitative analyses were performed on both the concentration distribution and the pressure gradient of particles in regimes of fixed bed flow, sliding bed flow and heterogeneous flow. Moreover, from the perspective of force analysis of particles, the law of sedimentation movement of particles is discussed, and the reason for the change in concentration distribution is explained. The research presented here provides insight into the internal structure of the flow and gives quantitative indications of pressure gradient and concentration distributions. (C) 2019 The Authors. Published by Elsevier B.V.