Abstract: Ensuring full contact between hot sinters and cooling gas is the key premise for the widespread application of vertical sinter cooling technology at an industrial scale. In this study, the gas–solid contact characteristics in a vertical sinter fixed bed were numerically investigated through a resolved CFD–DEM (computational fluid dynamics–discrete element method) method. The irregular sinter geometries were represented through the multi-sphere clumped method. The sinter packing in a vertical fixed bed was simulated via DEM modeling, and the immersed boundary method and dynamic mesh refining were employed in the CFD–DEM coupling to obtain a high-resolution fluid flow field around the sintered particles. The results showed that the average voidage of the dual-particle-size uniformly mixed bed generally decreased with the decrease in the average sinter particle size. The average bed voidage was mainly determined by the finer sinters, while the larger sinters mainly affected the large voidage structure and its distribution formed in the bed. Compared with the uniformly mixed bed, the segregated mixed bed exhibited a larger average voidage, and the voidage distribution also changed considerably. The fluid flow behavior in the mixed bed was largely influenced by the average bed voidage and the voidage distribution. As the average particle size decreased, the fluid flow in the bed became more uniformly distributed. Under different segregated packing situations, the bed voidage structures in the central zone and near-wall zone differed remarkably, with the fluid flow exhibiting a higher tendency to develop in the zone with larger voidage. The bed pressure drop generally increased with the decrease in the average sinter particle size. Among the uniformly and segregated mixed beds, the bed with “A-type” size segregation (i.e., finer sinters packed in the central zone while the larger sinters packed in the near-wall zone) showed the lowest overall pressure drop, but the particles inside the bed did not fully contact with the fluid. The bed with “B-type” size segregation (i.e., opposite of “A-type” segregation) exhibited both lower bed pressure drop and a desirable gas–solid contact condition. Therefore, “B-type” size segregation is recommended for the design of practical sinter packing in the vertical fixed bed. The experimental and simulated results showed similar bed pressure drops with increasing superficial air velocity. This validates the accuracy of the resolved CFD–DEM method applied in this study and lays an important foundation for the research of coupled gas–solid behavior in the vertical sinter cooling furnace.