Cyclone separator is a widely used mechanical equipment that removes solid materials from transport gas, and the separation characteristics depends heavily on material properties. Most separation objects commonly studied are micron-sized powders or particles of high density with the magnitude ranging from 10(2) to 10(3)kg/m(3). While the particle density of expanded graphite (EG), a new type of material that is widely used in industry, is only a few tenths of conventional materials. However, the cyclone separation of such ultra-light particle has not been studied so far. This paper, based on the computational fluid dynamics and discrete element (CFD-DEM) coupling method, performs simulation experiments of the ultra-light particle cyclone separation at different inlet velocities. The pressure and velocity distribution of the continuous phase in the separator are studied. The effects of ultra-light particles on the flow field are revealed. The particle flow patterns are obtained and the force characteristics of the ultra-light particle are analyzed. Simulation results are verified experimentally. The results show that the separation characteristics of ultra-light particles are different from that of conventional materials: a) the appearance of ultra-light particles has negligible effect on the flow field in the separator; b) the ultra-light particles can be completely separated even if the inlet velocity is low; c) when the inlet velocity is higher than 7.5m/s, "top ash ring" composed of ultra-light particles appears under the roof of the cyclone, and multi-helical particle stream is observed in the cylinder region; besides,some "stagnant" particles rotate horizontally in the cone separation zone; d) particle turbulent diffusions in the upper part of the cyclone become stronger first and then weaker as the inlet velocity increases; e) the gas-particle coupling force and collision force are much larger than the particle gravity, and collisions of particles with different sizes are the main cause of secondary particle breakage. (C) 2018 Elsevier B.V. All rights reserved.