The motion characteristics of particles in narrow inclined channels were analyzed. The relationship between the equilibrium positions of the particles and the particle size was established from the hydrodynamic description of the particles transported in narrow inclined channels. A novel theoretical model was proposed to describe the movement behaviour of particles. A new evaluation index, eta, was proposed to characterize the separation capacity of narrow inclined channels for handling particles. An experimental system was built to verify the model. The results indicated that the established model was proved to be highly accurate in prediction of particle size range of separation. Specifically, particles covering the full size range of 0-0.8 mm were conveyed to the overflow with almost 50% probability. The effective particle size range of separation increased greatly based on density. The studies are beneficial to the design of narrow inclined channels structure in industry as well as operation conditions. (C) 2019 Elsevier B.V. All rights reserved.