The invention relates to a device and method for treating radioactive poison residues. The device for treating the radioactive poison residues comprises a reaction device, an adsorption device and a negative pressure device which are communicated in sequence. A heating device and a spraying liquid adding device are arranged on the reaction device. The method for treating the radioactive poison residues comprises the steps that the temperature and negative pressure of the reaction device are adjusted, so that low-boiling-point matter in the reaction device is released and adsorbed in the adsorption device; the temperature and negative pressure of the reaction device are adjusted again, alkaline matter is sprayed into the reaction device, the alkaline matter and acidic matter in the remaining residues in the reaction device are subjected to a neutral reaction, and the acidic matter in the remaining residues is decomposed; the temperature and negative pressure of the reaction device continue to be adjusted, so that a product of the decomposed acidic matter volatilizes and is collected in the negative pressure device. According to the device and method for treating the radioactive poison residues, the problem about storage and treatment of the radioactive poison residues is solved, the risk that the radioactive poison residues escape out of a storage device in the storage process is avoided, and surrounding safety is ensured.