The invention belongs to the field of nuclear power, and provides an on-line repairing method for a nuclear power station metal pipeline. The on-line repairing method comprises the following steps that polishing and cleaning are conducted, specifically, a leaking point area of the metal pipeline is polished, a rusting material and antifouling paint on the leaking point area are removed, and the metal pipeline is subjected to cleaning to expose a metal layer and a leaking point of the metal pipeline; multilayer repairing is conducted, specifically, a multilayer repairing structure is made in the leaking point area through composite repairing steps; and solidification is conducted, specifically, the repaired leaking point area is subjected to standing and solidification for 20-30 hours. The leaking point area of the metal pipeline is polished, and the rusting material and the antifouling paint on the leaking point area are removed, so that repairing is directly conducted on the metal layer of the leaking point area, and the leaking point can be preferably blocked; the multilayer repairing structure is made through the composite repairing steps, and the standing and solidification are conducted for 20-30 hours; and by means of the multilayer repairing structure, and a higher pressure impact is borne, so that when the metal pipeline is used and pressure is applied, the leaking point can be blocked, leakage preventing is realized, and the normal operation of a nuclear power unit is guaranteed.