A method for purifying protein aqueous is provided. A protein aqueous is first provided. An absorption material is mixed into the protein aqueous to form a first mixture. The first mixture is separated into a solid-liquid two phases solution by a first separation process. A buffer solution is added into the solid phase from the solid-liquid two phases solution which has a target protein therein to form a second mixture. Then, a second separation process is performed to separate the second mixture to obtain a purified protein aqueous.