In this paper, the anticorrosion mechanism of Al-Ti-Si-RE coating in the environment of simulated deep sea was investigated using electrochemical measurement and micro-analysis. The result showed that Al-Ti-Si-RE coating performed better corrosion resistance at hydrostatic pressure than that at atmospheric pressure. After 480 h of immersion at 3 MPa, the anode of potentiodynamic polarization curve represented a linear because corrosion products blocked the corrosion channels. At the same time, at hydrostatic pressure, electrochemical impedance spectroscopy (EIS) indicated that Al passive film dissolved in the 6 h of immersion, then the coating tended to be stable, was hardly changed between 300 h and 480 h. To further analyze the original corrosion process, electrochemical noise (EN) of 0~64 ks at 0.1 MPa and 3 MPa was measured, which quantificationally represented the corrosion process from passive film dissolving to corrosion product fast-forming to stabilization. From morphology observation and X-Ray diffraction (XRD) analysis, the rich Ti phase (Ti-Al intermetallics etc.) of the coating with good corrosion resistance was cellular, whose construction could fix the Al oxide inside the coating, and made the coating thick in order to inhibit the corrosion.