Abstract: In order to analyze the structures of packed beds, the discrete element method（DEM） reveals great advantages for numerical simulation. There are only few particles at densest state in random packed beds. Porosity increases rapidly with the oscillation at near-wall region. More local microstructure information will be obtained with Voronoi tessellation. Packing characteristics at the bulk region is random and ordered at the wall region instead. With homogenization assumption at Voronoi tessellation, a heat transfer model is established which can take the conduction between adjacent spheres and thermal radiation heat exchange into account and the numerical results agrees well with the experimental data.