Abstract: Filiform corrosion often occurs at the damaged coating around the fastener and the aircraft skin edge, which is a special kind of crevice corrosion. The crevice in the head of filiform corrosion is simulated by finite element method based on Nernst-Planck equation. The results indicate that the pH value in the crevice initially drops and then rises over time, and finally stabilizes at about 5. 4 ~ 6. 0 under acidic conditions. The polarization curve measured in the solution with O₂ (pH = 6) is suitable for the boundary condition. The aluminum alloy interface in the crevice mainly involves anodic oxidation reaction of Al.The electrolyte potential in the crevice mouth is lower than that in the bottom of the crevice, the corrosion rate of aluminum alloy near the crevice mouth is much faster. Solid corrosion product Al(OH)₂Cl concentrates mostly in the bottom of the crevice, and the concentration of Al(OH)₂Cl increases over the reaction time. The potential has great influence on the expansion of filiform corrosion, the corrosion rate of aluminum alloy and the formation rate of Al(OH)₂Cl in the crevice exacerbate with the rising of potential. When the potential rises by 20 m V, the Al(OH)₂Cl concentration at the bottom of the crevice rises 5 times, which greatly accelerates the expansion of the filiform corrosion.