Disclosed is a dam concrete anti-ageing method. A polyurethane foam layer is coated on the surface of a concrete dam, after a dam heat-insulation and moisturizing layer is obtained, a polymer mortar layer is further covered on the concrete dam, and a dam heat-insulation moisturizing layer protecting layer is obtained; a layer of alkali-resistant fiberglass gridding cloth or an iron wire screen which is fixed by heat-insulation anchor bolts is laid outside the dam heat-insulation moisturizing layer protecting layer, another polymer mortar layer is covered on the alkali-resistant fiberglass gridding cloth or the iron wire screen, so that a protecting surface layer is obtained, and anti-ageing construction of a dam body is completed. In the technical scheme, the dam body is constructed, abilities including freezing and thawing resistance, leakage resistance, carbonized flow scouring resistance, abrasion resistance, cavitation resistance, durability, pressure resistance, crack resistance and impermeability of the dam body can be strengthened by the obtained protecting layer, and the protecting layer has the advantages that the protecting layer is attractive in appearance and fine in heat insulation and moisturizing performances, and does not pollute environments. The heat insulation and moisturizing performances are stable, and cannot be changed greatly along with weather change, and concrete cracks and concrete ageing due to change of weather conditions can be effectively controlled.