In this study, alumina green body was produced by water-based gel-casting. The alumina powder is mixed in a solvent, magnesium nitrate is used as a particle size inhibitor, and EDTA is used as a chelating agent. A monomer and an initiator are added to form a polymer as a binder. The green body formed by uniform dispersion has sufficient mechanical strength, density of 63%. After sintering at 1500 degree under air atmosphere, the sample has a uniform and dense microstructure inside. The particle size is about 2um, the relative density is 99.7%, and the hardness is close to 24GPa.