The invention discloses a preparation method of cellulose-based ion exchange fiber, which comprises the following steps: (1) dipping dried cellulose fiber dried with constant weight into acidic potassium permanganate solution, stirring the mixture, washing the cellulose fiber with water, and removing moisture to obtain cellulose fiber carried with MnO2; (2) putting the cellulose fiber carried with the MnO2 in acrylamide solution, adding a reducing agent, carrying out graft copolymerization in thermostatic shaking water bath for 3-5h, washing the obtained reaction product with water, removing the residual manganese ions after copolymerization, washing the reaction product with water again, and drying the reaction product until being in a constant weight state to obtain a graft polymer; and (3) adding the graft polymer to mixed solution of NaOH and NaClO, carrying out degradation reaction in the thermostatic shaking water bath for 0.5-2h, performing acid-washing on the graft polymer to remove the residual chlorine after reaction, washing the obtained graft polymer with water and drying the washed graft polymer until being in a constant weight state to obtain the cellulose-based ion exchange fiber.