Abstract: A method includes grinding alumina powder into alumina particles with ultrafine particle powder, performing a purification process so that the alumina particles have a purity greater than 99.999%, processing the alumina particles by a spray dryer, processing the alumina particles by a sheet molding compound to produce an alumina material, and placing the alumina material in a vacuum super high temperature furnace to have a crystal growth which includes placing the alumina material in a predetermined crucible in the vacuum super high temperature furnace, preburning the alumina material to form a half-baked alumina cake, heating and increasing a temperature of the alumina cake so that the alumina cake is disposed at a melted state until the crystal growth is finished, and curing the alumina cake that is melted so as to form a sapphire crystal.