Chain grate is a thermal equipment for drying and dehydration, preheating and oxidation of iron ore pellets, and the drying effect of pellets in down draft drying of chain grate directly affects the quality of pellets. Based on the theory of heat transfer, local non-equilibrium thermodynamic theories and the principles of drying kinetics, a computational fluid dynamics (CFD) model in the down-draft drying (DDD) of pellets is established. The drying process of pellets in the DDD is simulated by the method of CFD. A multi-targets orthogonal test is proposed, the orthogonal test targets for the utilization of heat energy are defined, and the parameter optimization scheme of pellets in the DDD is obtained. Under the optimized parameter scheme, the pellets layer in the DDD is advanced about 14s, up to 92% drying degree. So, a theoretical reference can be provided for the effective utilization of thermal energy in the DDD of chain grate.