In order to study the effect of sodium benzoate content in ethylene glycol aqueous solution on the corrosion of 3A21 aluminum alloy, and provide data support for predicting the corrosion change law of ethylene glycol aqueous solution system with long-term service and sodium benzoate. The microstructure of 3A21 aluminum alloy before and after corrosion was characterized by SEM based onethylene glycol aqueous solution with ethylene glycol mass fraction of 36wt.%. The electrochemical corrosion behavior of 3A21 aluminum alloy with sodium benzoate mass fraction of 0~1.80wt.% was studied by open circuit potential (OCP), AC impedance spectroscopy (EIS) and potentiodynamic polarization technology. During 1 h of stabilization, the open circuit potential of 3A21 aluminum alloy shifted toward more positive values at the end of the immersion period. When the mass fraction of sodium benzoate is inthe range of 0-1.80wt.%, the change of sodium benzoate mass fraction in ethylene glycol aqueous solution did not change the reaction mechanism of anode and cathode, showing the same corrosion behavior. when the mass concentration of sodium benzoate was small, the adsorption film formed on the metal surface was not complete, with the increase of sodium benzoate mass fraction in the system, the adsorption film gradually became dense and complete, so the inhibition effect was enhanced and the self-corrosion current density was significantly reduced. The self corrosion potential showed positive and negative shifts, meanwhile, the self corrosion current density of 3A21 aluminum alloy decreased, From 409.89 nA/cm2 at 0 to 220.92 nA/cm2 at 1.40wt.%. The change of sodium benzoate concentration in the system did not lead to the change of impedance spectrum shape. There was only one time constant in the impedance spectrum, which showed a semicircular capacitive reactance arc reflecting the resistance capacitance relaxation process composed of charge transfer resistance and electric double-layer capacitance. Because sodium benzoate was adsorbed on the surface active point or the whole surface of the metal matrix, the transfer of charge or substance related to corrosion reaction was hindered. The charge transfer resistance increased with the increase of sodium benzoate mass fraction in the system, from 112.45 kΩ/cm2 at 0 to 204.82 kΩ/cm2 at 1.40wt.%. SEM test showed that the surface of 3A21 aluminum alloy was relatively flat, but some corrosion problems were also observed. There is only a small amount of local corrosion on the surface of 3A21 aluminum alloy sample. Therefore, the corrosion of 3A21 aluminum alloy in ethylene glycol aqueous solution is mainly uniform corrosion. In addition, the addition of sodium benzoate can reduce the corrosion rate of 3A21 aluminum alloy. Within the selected test concentration range, with the increase of sodium benzoate concentration in ethylene glycol aqueous solution, its corrosion inhibition effect on 3A21 aluminum alloy increased. For the long-term service ethylene glycol aqueous solution system containing sodium benzoate, the corrosion law can be predicted by tracking the attenuation change of sodium benzoate concentration.