Abstract: In order to understand the corrosion failure of cementing accessories（ball seat, floating collar） in ultra-deep well environment, a high temperature and high pressure reactor was used to simulate the ultra-deep well environment（220 ℃,30%NaCl, pH value of 14）. The corrosion behavior of 2A12 aluminum alloy in ultra-deep well environment was studied by mass loss method, scanning electron microscope（SEM）, X-ray diffractometer（XRD） and energy dispersive spectrometer（EDS）. The results show that the corrosion products of the alloy are mainly Al₂O₃, Al（OH）₃, NaAlO₂ and NaAl₅O₈（β''-Al₂O）,etc, and the corrosion products change with the corrosion reaction. The corrosion process starts from local alkaline pitting corrosion, gradually develops into intergranular corrosion and finally evolves into stress corrosion, and corrosion cracking occurs. With the extension of corrosion time, the microcracks on the surface of 2A12 aluminum alloy gradually increase and widen. The corrosion resistance of 2A12 Al alloy in ultra-deep well environment can be improved by preparing anti-corrosion film on 2A12 aluminum alloy substrate.