A parallel simulation of the gas-solid motions in a 3-D full-loop dual-side refeed circulating fluidized bed (DRCFB) is carried out by using Large-eddy Simulation coupled with Discrete Element Method (LES-DEM), in which the gas and the solid motions are solved under the Eulerian and the Lagrangian frames, respectively. The start-up flow patterns, the time-related solid phase properties about solid cycle time and solid residence time (SRT) distributions, and the improvements of gas-solid flow uniformity are explored. Furthermore, the influences of different operating conditions on the time-related solid phase properties are discussed. The results demonstrate that the transient pressure drop is a criterion for determining steady state in the start-up process and the fluctuations under different superficial velocities differ. The solid cycle time and the SRT distribution curves show a feature of early peak with an extended tail, which indicates that the solid flow exhibits a back-mixing phenomenon. The averaged solid cycle time in the whole system and the averaged SRT5 in the three components (i.e., riser, cyclone, and dipleg) show distinct characteristics under different operating conditions. Moreover, nearly 70% of the solid cycle time elapses in the riser and 25% of that elapses in the dipleg while only 5% of that elapses in the cyclone. Finally, the dual-side refeed structure remarkably improve the gas-solid flow uniformity (i.e., homogenous) in the DRCFB riser, especially in the inlet and outlet regions. (C) 2016 Elsevier B.V. All rights reserved.