The invention discloses a nuclear power station conventional island desalted water distribution system full-stop overhauling method. The method comprises the steps that A, ice blockage is carried out on a main pipeline between a conventional island desalted water distribution system and a unit, and an isolating device and a connecting device are additionally arranged at the downstream part of ice blockage; B, a temporary water supply pipeline is connected to the connecting device from an SED, operation verification is carried out on the temporary water supply pipeline, and the temporary water supply pipeline is communicated with the main pipeline between the conventional island desalted water distribution system and the unit through the connecting device after the temporary water supply pipeline is qualified; C, the connecting device is opened to supply water to the unit, and then the isolating device is closed; D, the conventional island desalted water distribution system is made to stop fully, isolating and emptying are carried out, and damaged or aged devices on the main pipeline are replaced; E, a drain valve and a vent valve are opened fully, the system is filled with water, air in the system is exhausted, the system is washed, samples are taken for a laboratory test, and after the samples are qualified, the drain valve is closed, and the conventional island desalted water distribution system is put into operation; F, the connecting device is disconnected with the temporary water supply pipeline, and the connecting device is sealed. The nuclear power station conventional island desalted water distribution system full-stop overhauling method is convenient and rapid to implement, safe and low in cost.