Solids oscillation circulation is an unstable solids flow behavior exhibited during the start-up process of a circulating fluidized bed (CFB) with sweeping bend return. It results in significant pressure fluctuation and particle loss, further brings about difficulties in establishing a stable solids circulation and blockage of the heat exchanger for recycling gas. However, the oscillation mechanism and hydrodynamic characteristics of the solids oscillation circulation are still far from understanding, since the variation of solids transfer rate, gas flow rate and their complex interactions are still unknown. In this work, the Eulierian-Eulerian method has been employed for the simulation of solids oscillation circulation in a two-dimension (2D) CFB. The results indicate that solids oscillation circulation is triggered by the formation of slugging in the downer, which leads to a decrease of the downer pressure drop and a sharp increase of the riser bypass gas velocity. Besides, intense slugging fluidization is observed in the downer at larger valve opening or higher inlet gas velocity. Moreover, statistical hydrodynamic shows uniform lateral solids volume distributions in the riser and downer. Solids fluctuating energy spectrum is generated to explore the turbulent characteristics, a segment phenomenon is observed in the inertial sub-region. In addition, the deviation of scale index in the inertial region form the Kolmogorov -5/3 scaling law indicates the flow intermittency. According to the wavelet analysis of particle fluctuation velocity, the particle-particle and particle-wall interaction are found to be the main reason for the flow intermittency. (C) 2016 Elsevier B.V. All rights reserved.