A method is provided for purifying a recombinant protein from a mixture comprising the recombinant protein and related proteins, comprising the steps of: A. using a first equilibrating buffer in a first conductivity and pH to make the recombinant protein bind to an ion exchange medium; B. using a second equilibration buffer in a second conductivity and pH to continually equilibrate the ion exchange medium bound to the protein; C. using a washing liquid in a third conductivity and a gradually increasing pH to wash the ion-exchange medium, and eluting the first category-related proteins; D. using a first eluent in a fourth conductivity and pH to elute the ion exchange medium, and eluting the target recombinant protein; and E. using a second eluent in a fifth conductivity and pH to continually elute the ion exchange medium, and eluting the second category-related proteins.