The effects of particle size distribution (narrow, Gaussian, binary and flat) on high-temperature defluidization behavior of iron powder were investigated. The fluidization characteristics were studied involving minimum fluidization velocity, bubbling velocity and bed voidage. The thermo-mechanical analysis was applied to examine the sintering temperature and surface viscosity of iron powder due to surface softening. The results indicated that the effects of PSD on defluidizaton were dependent on temperature. The Gaussian distribution was favorable to fluidization and presented better fluidization quality at lower temperatures. However, at higher temperatures, the narrow distribution exhibited a higher defluidization temperature and thus a lower agglomeration tendency due to a larger apparent viscosity and lower particle stickiness. Therefore, the PSD apparently affected not only hydrodynamic behavior, but also particle adhesion of bed materials for defluidization.