The invention discloses a method for treating radioactive wastewater. The method for treating the radioactive wastewater comprises the steps of firstly carrying out reverse osmosis treatment on the radioactive wastewater, then enabling the radioactive wastewater to enter a continuous electrodeionization unit to be treated, and further removing radionuclide so as to enable treated wastewater to reach discharge requirements; and respectively filling different mixed ion exchange resin in a plain water chamber and a thick water chamber in a continuous electrodeionization membrane stack of the continuous electrodeionization unit, wherein mixed ion exchange resin filled in the plain water chamber comprises, by volume ratio, 30%-60% of strong-acid cation exchange resin, 40%-60% of strong-base anion exchange resin, and 0%-30% of weak-base anion exchange resin, mixed ion exchange resin filled in the thick water chamber comprises, by volume ratio, 20%-50% of strong-acid cation exchange resin, and the balance strong-base anion exchange resin. A weak dissociation polymer portion is used for improving selectivity of continuous electrodeionization membrane stack to trace amount radionuclide, radionuclide with extremely concentration can be effectively removed, and the method for treating the radioactive wastewater ensures that the final discharged water satisfies the discharge requirements.