A cold state iG-CLC system was built consisting mainly of a two-stage counter-flow moving bed air reactor (AR), a circulating fluidized bed riser fuel reactor (FR), a separator, a loop seal and a downcomer. Experiments were carried out to study the operation performance in terms of solid circulation, pressure fluctuations and gas-solid flow characteristics under different operating parameters in the whole system. Results show that two-stage AR operation did not affect quasi-stable solid circulation, and there was almost no gas leakage between the FR and AR under the solid circulation rate of 50 kg/m(2) s condition, indicating independent operation of the two reactors. The FR pressure drop per unit length Delta p/Delta z in the upper part of the FR was smaller than that in the lower part. Due to higher solid concentration, Delta p/Delta z increased with a decreasing FR fluidizing number, or an increasing solid circulation rate and initial solid bed height. The particle cluster movements in the FR were the main cause of pressure fluctuations, and periodical pressure peaks occurred when the FR superficial gas velocity was too low. The pressure drop ratios between the downcomer and FR decreased with a decreasing FR superficial gas velocity, or an increasing solid circulation rate and initial solid inventory. The moving bed state and fast fluidization state were achieved in the downcomer and CFB riser, respectively. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.