A horizontal multi-tube circulating fluidized bed is designed and built to study the particle distribution in the horizontal tube bundle. The effects of the operating parameters, such as circulation flowrate, amount of added solid particles, diameter and density of particles on the fluidization and distribution of solid particles in the horizontal tube bundle are systematically investigated by using the image measurement and acquisition system of a charge coupled device (CCD). Experimental results show that the particle distribution in the horizontal tube bundle is non-uniform. The solid holdup of particle is higher near the bottom of the tube bundle and lower near the top. The non-uniform degree decreases with the increasing of the circulation flow rate and the amount of added solid particles. The particles with smaller diameter and density are fluidized better and well distributed in the horizontal tube bundle and in a single tube. The phase diagrams are established to show the variation ranges of the operating parameters for more uniform particle distribution and relatively high solid holdup in the tube. High turbulent extent of water flow results in more uniform particle distribution in the horizontal tube. The results may be used to further solve the particle distribution problems in the horizontal tube bundle. (C) 2016 Elsevier B.V. All rights reserved.