This study focused on investigating the corrosion behavior of 3A21 aluminum alloy in a high-temperature deoxygenated ethylene glycol solution. The analysis was conducted using 3D laser scanning confocal microscope, scanning electron microscope, and electrochemical tests. The findings revealed that the ethylene glycol solution initially inhibited the anodic dissolution of the aluminum alloy, and the formation of an oxide film through Al-alcohol compounds provided effective protection for the matrix, resulting in good corrosion resistance of the alloy. However, as the immersion time at high temperatures increased, certain changes were observed. The low-frequency impedance and capacitance arc diameter of the aluminum alloy in the Nyquist diagram decreased, while the corrosion current density gradually increased, indicating a gradual deterioration in corrosion resistance. Concurrently, the pitting corrosion potential (Eb) gradually decreased, indicating an increased susceptibility to pitting corrosion. The corrosion pits also developed further in-depth, leading to an overall increase in the corrosion rate of the alloy.