This research used Ceramic Injection Molding (CIM) formulation technique of ceramics/polymers, selecting two Al2O3 powders (α- and θ-Al2O3), kneading of several polymers with the ceramic powder, and extruding to produce feedstocks and filaments, which was used for 3D additive manufacturing. Four tasks were completed. First, PP as the major binder, replaced with some EVA, to improve the flexibility of the filaments. The compatibility of PP and EVA was also investigated by grafting maleic acid (MA) on PP chain to reduce different polarity between PP and EVA. The third task was to study the dispersion condition of the alumina powder in feedstocks, and quantitatively investigated the influence by kneading sequences, solid content, and other processing parameters. After optimization the processing conditions, the made alumina parts were densified to a relative density better than 98% in a linear sintering shrinkage of 16%-21%.