As the main by‐product in the iron‐making process, blast furnace slag (BF slag) contains a high amount of sensible heat which is a potential heat source with great value if treated properly. Although several technologies have been investigated during recent decades, few of them can be commercialized successfully. In the previous study, we developed a rotating multi‐nozzle cup atomizer (RMCA) for granulating the molten slag. The particle size distribution of the produced slag particle is narrow, the shape is spherical, and the degree of non‐crystallization is over 95%. In the current study, the models of the disintegration mechanism, the traveling trajectories and the temperature profile of the slag droplet are established. The particle size is analyzed theoretically and then compared with experimental results. It is found that the predicted results agreed with the experimental results very well. The models can provide guidance for designing commercialized atomizer and optimizing the operation parameters.