Methane/hydrogen mixed combustion can effectively reduce carbon emissions and improve combustion efficiency, and a randomly packed bed can further promote its uniform temperature distribution. Therefore, a randomly packed bed model was established based on the discrete element software EDEM and the three-dimensional modelling software SOLIDWORKS, and the premixed combustion process of methane/hydrogen/air was simulated, and the flame structure, component distribution and vorticity evolution in the randomly packed bed were analyzed at different moments. The results show that the excellent heat storage capacity of the spheres raises the temperature of the unburned zone by more than 400 K, which makes the methane/hydrogen mixed combustion more stable. After increasing the hydrogen content ratio, the temperature of the unburned zone stays above 600 K, which further improves the stability of the combustion. Meanwhile, the splitting and perturbation effect of the spheres on the mixed gas makes the flame surface wrinkled and the average vorticity increase, which results in a more homogeneous flame structure and temperature distribution.