In the next generation high-temperature solar thermal power system, solid particles are the dominant heat absorbing fluid. Special heat exchangers need to be developed for the energy transmission between particles and other functional thermal fluids, considering the poor fluidity of solid particles. Shallow fluidized bed with immersed pipes is a promising technology for extracting heat from high-temperature particles. However, there is still a lack of unanimous criteria for the optimization design of such devices, especially when non-homogeneous particles with great economic benefits are used. As the first step in the research and design program, the fluidization characteristics of polydisperse bauxite particles in a three dimensional shallow fluidized-bed with built-in tubes were investigated via cold state experiments. Bed pressure drops were measured under five different perforated plate distributor with a range of open area ratio from 0.38% to 2.89%. The effects of open area ratio, static bed height and air distribution mode on the characteristic parameters and quality of the fluidization were also investigated. The results showed that there was no obvious abrupt change in the bed pressure drop curve of the non-homogeneous particles, and the whole process could be divided into three stages: fixed bed, semi-fluidization and complete fluidization. The open area ratio had little influence on the characteristic velocities at the boundary of two adjacent stages. For the concerned non-homogeneous particles, the change of standard deviation of bed pressure drop showed a minimum value, and the fluidization stability became the highest when plate with an opening area ratio of 0.79% was used. The air distribution mode has an important influence on the local bed pressure drop in the multi-chamber fluidized bed. The uniform velocity mode could effectively reduce the pressure drop difference between chambers and improve the uniformity of the overall fluidization zone.