In forming of MgO-C system material composed of coarse grain aggregate and fine grain matrix, green body bulk density increased in a quadratic function with compaction stress of 5 levels in the range from 3 to 215 MPa, as same as case of a uniaxial continuous compaction up to 120 MPa of the same material. Quantitative analysis through visualization of 3-dimensional packing structure of the coarse grain （aggregate） part using X-ray computed tomography clarified that disappearance of large size pores corresponding to the grain size and rearrangement of the grains occurred initially, followed by increase in the number of grains per unit volume with decreasing the inter-grains distance with remaining almost original shape of the grain during increasing stress within the applied range. The mechanisms controlling the compaction process were discussed based on an extended type of Cooper-Eaton formula using a functional volume compaction.

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