Abstract: The fluidization of cohesive particles of different sizes shows that the fluidization characteristics are greatly affected by the size of particles.The smaller the size of particles,the larger the interparticle forces,and the worse the fluidization behavior.The natural agglomerate number Ae_n and the fluidized agglomerate number Ae_f，which can be used to describe the fluidization behavior of particles,are proposed on the basis of balance of forces between the agglomerate and the outer-most cohered particles.The calculation of the fluidzed agglomerate number Ae_f shows that cohesive particles can be fluidized if the fluidized agglomerate number Ae_f≤40000．