By modifying the composition and rheology of refractory powder materials, it is possible to increase the compressibility, thereby reducing its relative porosity which improves their corrosion resistance and final mechanical properties. This work describes a method for simulating the cyclic densification behavior of MgO-C brick powder composites by the Discrete Element Method (DEM), represented as coarse MgO cluster particles ( 1 to 4mm size), fine MgO particles (<100 µm) and graphite flakes. The content of the resin binder is represented in the model as an elasto-plastic shell covering the particles. MgO clusters and graphite are modeled as single particles connected by elastic bonds, and MgO particles as non-bonded particles to represent a typical granular green microstructure. The initial numerical composite assembly is obtained by first randomly locating particle clusters and non-bonded single particles in a parallelepipedic periodic cell. Next, the microstructure is jammed up to a relative density of 60% and compacted. The composite relative density is measured along with the experimental compaction cycles and compared with simulations. A total of four cycles with increasing pressure are performed to replicate the industrial pressing. The numerical samples are uniaxially compacted with a low strain rate in the axial direction to ensure quasi-static conditions up to a given stress. Samples are unloaded to a 1 MPa pressure and then reloaded to a larger stress. The cycle is repeated three more times with increasing reloading stresses. Experimental and simulation results show that the material hardens with the increase of the pressure at each cycle, with some hysteresis. The plastic deformation energy at each cycle is calculated and may be associated with the refractory discontinuity (porosity), composition, and microstructure. The increase in fine MgO particle composition may increase the ability of the composite to densify, due to better particle rearrangement, and decrease the hysteresis extent during unloading. The coarse MgO particle size distribution is also investigated to study its effect on the composite densification behavior. Based on scanning electron microscope observations of the powder mix before compaction, dead-burned magnesite (MgO) grains present some micro-cracks. This may be explained by the production of natural magnesia from raw stones of magnesium carbonate. Because some MgO grains exhibit a very irregular shape, the effect of irregular shapes of MgO clusters on the composite densification and hysteresis area during cycles is investigated. For this, some clusters are uniaxially or isostatically compacted with various stress states, breaking some bonds and consequently generating less spherical shapes. Numerical compaction simulations of composites with perfectly spherical particle clusters and simulations with non-spherical clusters are compared to investigate whether the shape of coarse MgO particles could impact the densification behavior of the composites. This work allows a better understanding of the effects of microstructure and composition on the densification and hysteresis of MgO-C refractories during cyclic loading-unloading cycles. Similarly, it paves the way for optimized models of refractory compositions,  which take into account grain shapes and particle size distribution to anticipate the effect of these parameters on the final mechanical properties.