A down-flow circulating fluidized bed evaporator is designed and built to investigate the liquid-solid two-phase flow pressure drop. With POM, 20%PA66 and glass bead particles as the solid phase, the effects of the amount of added particles, circulation velocity and particle types are investigated by pressure sensors. The research results show the pressure drop of liquid-solid two-phase flow is always greater than that of single-liquid-phase flow in the downer. The maximum pressure drop ratio ranges from 16.9% to 32.0% for the selected particles. The pressure drop of the liquid-solid two-phase flow increases with the increase in circulation velocity in the down-flow bed. The pressure drop ratio fluctuates with the increase of the amount of added particles, circulation velocity and settling velocity of the particles. The difference in pressure drop ratio generally decreases with the increase in circulation velocity, and decreases or fluctuates with the increase in the amount of added particles, depending on circulation velocity. Three dimensional diagrams are established to display the variation ranges of the operating parameters for the pressure drop and pressure drop ratio in the down-flow bed. The research results can provides some reference to the application of the fluidized bed heat transfer technology in industry. (C) 2020 Elsevier B.V. All rights reserved.