The invention relates to low-acidity highly corrosion-resistant treatment fluid for rusted surfaces, which comprises, by weight: 0.5-1% of tannic acid, 2-4% of citric acid, 0.5-1% of sodium molybdate, 0.1-0.2% of cupric nitrate, 0.5-2% of zinc dihydrogen phosphate, 1.5-3% of oxalic acid, 1-3% of phosphoric acid, 1-1.5% of hydrochloric acid, 0.5-1% of sulfosalicylic acid, 2-5% of polyethylene glycol 200, 3-5% of isopropanol, 1-2% of zinc layer corrosion inhibitors, and 72.3-86.4% of water. The treatment fluid for rusted surfaces of the invention can complete cleaning, rusted layer chelating conversion, iron zinc layer phosphatization and surface conditioning in one step, so as to remove scale cinder on metal surfaces, to generate a surface composite protective layer of a phosphating film and a chelating conversion film, and to improve the corrosion resistance of metal. The treatment fluid of the invention has the advantages of cleanness, no pollution, rapid film formation, strong penetration, strong binding force, good corrosion resistance, simple operation, low cost, and the like, and is suitable for rusted or corroded substrates with a rusted layer thickness of 0-50 um.