Abstract: In order to elucidate the influence of particle size distribution on the internal meso-mechanical behaviour of the iron powder compaction system, based on discrete element method (DEM), a compaction model was established by changing the particle size distribution of iron powder particles. Combined with the force chain extraction method, the influence mechanism of particle size distribution on the evolution of force chains was explored by analyzing the spatial distribution of force chains, the number of force chains, the length of force chains and the directionality of force chains. The findings reveal that the spatial distribution of force chains created by powders with varying particle sizes is different. The force chain distribution created is more concentrated the smaller the particle size distribution range is. On the other hand, the larger the size distribution range is, the more loose and uniform the force chain distribution is. The particle size distribution also has an effect on the number of force chains, which is manifested in that the total number of force chains gradually decreases with the increase of the particle size distribution range of the powder. The particle size distribution of the powder has a significant effect on the number of short force chains formed by the particles, but has a limited effect on the length of the force chain. With the increase of the particle size distribution range, the direction of the force chain is gradually concentrated from a uniform distribution to a specific angle direction, showing a certain anisotropy, and the formed cross force chain network structure is conducive to improving the degree of powder densification. This paper provides a basis for expanding the meso-mechanical theory of powder compaction from the influence of powder particle size distribution, and also provides guidance for further improving the powder densification behaviour by combining the powder particle size distribution and the evolution process of the internal force chain in the system.