Abstract: Salt fog corrosion tests were employed to observe the corrosion behavior of welded joint of A7N01S-T5 aluminum alloy for high-speed train. The results showed that many corrosion products and pits distributed on the surface of the welded joint. The deepest corrosion pit was in the area of heat affected zone (HAZ), the depth of the corrosion pit was 35.4μm, the corrosion area ratio was 43.6%. The corrosion mechanism of the welded joint was pitting corrosion first, and then came to denudation corrosion with the depth of the corrosion pit spreading into the inner surface of the joint. The grains of the HAZ zone were coarsened with the influence of the partially overhent in the welding, and the HAZ was very sensitive to corrosion in welded joint in the salt fog corrosion test.