Abstract: Two kinds of corrosion polarization diagrams were used to describe the corrosion kinetics of alloys. They have different coordinate systems. One is the coordinate system where the coordinates are the potential and the current on the unit area of alloy surface, the other is the coordinate system where the coordinates are the potential and the true anodic and cathodic current density. The former is called the apparent corrosion polarization diagram of alloys, and the latter is called the true corrosion polarization diagram of alloys. The effect of cathode-to-anode area ratio on the corrosion kinetics of an alloy was studied under activation polarization control. Combining the apparent with true polarization diagram, not only the corrosion rate of the alloy can be expressed directly, but also the mechanism of the corrosion cell can be analyzed clearly.