Abstract: Based on particle flow code (PFC^2D), we set up two models of slag mixture with different granular composition using balls and clusters to model slag granules respectively, and studied stress-strain, force chain, granule motion and breakage in confined compression tests. The results show that the stress-strain relations are more close to actual by using clusters to model slag granules. In the loading process, force chains first increase, afterwards rapid change with granule breakage, and soon spread to the whole system. Meanwhile, the skeleton construction adjusts accordingly. These also correspond well to granular angular separation, location moving and pore filling. Consequently, the process of slag mixture's compaction- breakage- recompaction are good represented.