Abstract: Geldart Group C powders are inherently cohesive due to the strong interparticle forces, leading to severe agglomeration and poor fluidization capability. In this study, fluidization of nano-modulated Group C particles was investigated numerically. These particles, also known as Group C+ particles, were obtained through the nanoparticle modulation technique, with which a small fraction of nanoparticles were vigorously mixed with Group C particles so that they are adhered to the surface of the much larger Group C particles. After modification, the cohesiveness of Group C+ particle was significantly weakened, and therefore these particles could exhibit much better fluidization quality. However, the still existing cohesion resulted in the formation of small agglomerates within the system. To understand the internal agglomeration mechanisms of Group C+ particles and their impact on fluidization behaviors, a new drag model was proposed based on experimental results and the postulation of particle agglomeration. The numerical results of the cases employing the new drag model agreed well with the experimental data in terms of total and dense phase expansion. These findings revealed the drag mechanism associated with modified Group C particles, contributing to the understanding of ultrafine particle fluidization.