A heat transfer model based on the discrete element software EDEM and the secondary development tool C++ is developed to simulate the mixing and heat transfer process of particles under different parameters. This model is validated by comparison with experimental data and proved reasonable. It aims to study the heat transfer law of flowing particles in an externally heated rotary kiln and reveal the correlation between mixing and heat transfer from the mechanism. The results show that the combination of the total contact area between adherent particles and the drum wall, the mean temperature difference between adherent particles and the drum wall, the total contact area between particles, and the mean temperature difference between particles affect the heat transfer process. Changes in the temperature differences caused by the mixing rate dominate the heat transfer at different speeds or filling rates.