The present invention relates to a method and apparatus for solidifying radioactive waste accompanying chlorine recycling or radioactive iodine removal. The present invention provide a method and apparatus for treating radioactive waste composed of volatile metal halide with high corrosiveness at a high temperature through a solidifying system including crushing, mixing/dehalogenating and sintering. In the inventive method and apparatus for solidifying radioactive waste, a dechlorination process by using a dehalogenation material is performed on highly corrosive metal salt under an oxidizing atmosphere by using a method of controlling a temperature on the surface of a reactor, and solidification is carried out by removing radioactive iodine while reusing chlorine contained in an exhaust gas. Accordingly, the generated amount of total waste can be reduced, and therefore the inventive method and apparatus can be usefully used in preparing a solidified body with high durability.