The invention discloses a method for improving corrosion resistance of zinc aluminum alloy through thermal treatment. The method comprises the following steps: performing solid solution treatment on the zinc aluminum alloy under the temperature of 280-360 DEG C for 8-16 hours; and performing water quenching water the solid solution treatment, wherein an equiaxial fine grain microstructure, comprising a metastable alpha 2 phase, an equilibrium alpha 1 phase and an eta phase, is provided to the zinc aluminum alloy; the electrode potential of the alpha 2 phase is between that of the alpha 1 phase and that of the eta phase, so that the potential difference between micro primary cells formed by different phase structures can be effectively reduced, and as a result, the corrosion resistance of the zinc aluminum alloy can be greatly improved. According to the method, the zinc aluminum alloy prepared by the method is soaked in 3.5wt.% of NaCl aqueous solution, the weight loss speed is 0.6-10<-4>g.cm<2>.d<-1>, the corrosion potential is -1.116V, and the corrosion current density is 2.24*10<-7> A.cm<-2>. Therefore, the corrosion resistance of the alloy is greatly improved.