Abstract: A hydrodynamic model of liquid-solid circulating fluidized bed is proposed to predict the slip velocity between fluid and solid particles and bed voidage by applying the theory of two-phase flow.The slip velocity can be represented by the following equation.u s =u-v=(1-ε)(ρ p -ρ f )g+F p -(1-ε)F f /εβ/εExperiments were carried out by using water and ceramic spheres,1.43 and 3.06 mm in mean diameter in a circulating fluidized bed of 31 mm diameter and 1700 mm height.The voidage was from 0.96 to 1,and the ratio between superficial liquid velocity and particle terminal velocity varied from 1.22 to 10.1 in the experiments.The fluid-particle interphase drag coefficient in the model was correlated from experimental data as followsd p βρ f =0.1881(1-ε) 1.0089 UU t -0.8043 d p D t -0.3228 The predicted values by the model proposed agreed with the experimental data well.In the meantime,the variation of slip velocity with superficial liquid velocity,bed voidage and particle diameter was discussed.The results showed that the model in the paper can well predict the hydrodynamics of liquid-solid two-phase flow in circuiating fluidized bed.The model is suitable for liquid-solid circulating fluidized bed under high flow rate and low concentration and can be also used on each tube in liquid-solid circulating fluidized bed heat exchanger.