To solve the problem of granulating with different magnitude sizes of particles in the drum mixer, the existing calculation formula of liquid bridge force was modified and the corresponding discrete element model was established in this work. Through the combination of experimental test and simulation, the influence of the correction coefficient on particle motion was discussed, and the correction coefficient of 0.6 was found to be suitable. Taking the accumulation angle of the iron ore powder mixture as a reference, the physical property parameters of the mixture were obtained through simulation and experimental tests. On this basis, the movement law, agglomeration mechanism, and the distribution of agglomerates of iron ore powder mixture were discussed. The results showed that the larger the spin velocity and the smaller the sheer force of agglomerate powder, the more favorable the granulation was. The particle size of agglomerate increased first and then decreased along the radial direction of the cylinder, and there was an "efficient granulation zone" under the surface layer of the mixture, in which the particle size of agglomerates was the largest, the shear force was the least and the spin velocity was high. It was suggested that the collision frequency or energy loss of the agglomeration particle can be used as the criterion to stop the agglomeration of particles, to achieve the purpose of energy-saving. The conclusions can provide a design basis for the research and development of iron ore powder drum mixer.