The invention discloses a protective structure for protecting in-core instrument wires and a protection method of the protective structure. The protective structure for protecting in-core instrument wires comprises an upper supporting column belonging to an upper reactor internal, and further comprises a casing part used for protecting the in-core instrument wires, wherein in the working period of a nuclear reactor, the casing part is positioned in the upper supporting column, and the in-core instrument wires are positioned in the casing part. The protective structure is characterized in that in the nuclear reactor maintenance period, the in-core instrument wires are static relative to the upper supporting column and are wholly lifted along with the reactor internal and the upper supporting column; and the casing part can penetrate through the lower end of the upper supporting column to freely move to the lower side of the upper supporting column and then cover the tail end of the in-core instrument wires.