The invention discloses an anticorrosion aluminum alloy surface treating agent. The agent is composed of the following raw materials in parts by weight: 0.1 to 0.2 part of cobalt chloride, 1.6 to 2 parts of hydroxyethylidene diphosphonic acid, 0.1 to 0.16 part of tricalcium silicate, 0.4 to 1 part of malic acid, 0.7 to 2 parts of ammonium octamolybdate, 1 to 1.6 parts of borax, 0.2 to 0.4 part of magnesium sulfate, 1 to 1.7 parts of sodium pyrosulfite, 0.1 to 0.2 part of polybenzimidazole, 0.1 to 0.2 part of butyltin mercaptide, 0.1 to 0.3 part of trimethyl hydroxyethyl ethylenediamine, 2.6 to 4 parts of glycol, 2 to 3 parts of film-forming auxiliary agent, 16 to 20 parts of silane coupling agent KH560, and 100 to 140 parts of deionized water. Water is taken as the solvent, and each raw material is reasonably compounded, so the compatibility is good, and turbidity or flocculation will not be generated in the interface. Moreover, the surface treating agent has a very high adhesive performance, and the formed membrane is stable and environment-friendly.