The gas flow resistance in the packed bed of multi-size irregular particles applied in the sinter vertical cooling process is measured experimentally to analyze the effect of the equivalent particle diameter (d(p,m)) and the particle size distribution on the permeability and resistance characteristics. Results show that the flow resistance per unit bed height (Delta P/L) decreases with the reduction of d(p,m). However, the decrement of Delta P/L ascends first and then descends due to the comprehensive influence of the bed voidage and the particle size distribution, which is quite different from that in the mono-size sinter bed. Compared to the mono-size sinter packed bed, the bed permeability of the multi-size sinter mixture is lower under the same equivalent particle diameter. The particle size distribution of the multi-size sinter mixture has a great impact on the gas flow regime, especially at the low gas velocity. This makes the gas flow resistance in the packed bed of the multi-size sinter bigger. Since the mean error of the previous resistance correlations is greater than 44.79%, the resistance correlation applicable for the multi-size sinter is obtained by modifying the Ergun equation with the mean error less than 10%. (C) 2021 Elsevier B.V. All rights reserved.