The hydrodynamics of a three-phase internalloop airlift reactor with large particles was experimentally investigated.Effects of superficial gas velocity and solid concentration on the expanded bed height，circulation liquid velocity and distribution of solid holdup were studied.The results suggest that the flow in the reactors can be divided into three regimes，namely the fixed bed regime，fluidized bed regime and circulating fluidized bed regime.The flow character in each regime is quite different.Both the minimum fluidization gas velocity and the minimum circulation gas velocity increase significantly with the increase in solid concentration.A mathematical model based on the existing model for a three-phase fluidized bed and the characters of the airlift reactor was proposed to predict the minimum fluidization gas velocity and the minimum circulation gas velocity in the three-phase airlift reactor，and a good agreement between the calculated and measured values was obtained.