Advanced and reasonable process design is the essential for a pelletizing plant to achieve production and efficiency. Understanding the heat & mass flow and its interaction can be more clearly utilizing process simulation. Based on bed mass-heat transfer models, the process simulation packages for grate-kiln and straight grate iron ore pelletizing systems are developed. The steps, essential control strategy and algorithm for simulation, as well as its applications, are described in the paper. Furthermore, the simulation examples as well as the comparisons with dedicated laboratory testing results for the illustrated typical grate-kiln and straight grate process are given in the paper. The comparison results show that the process simulation not only can transform process design from empirical to digital, but also can provide guidance for process optimization and production operation.