Taking the susceptibility of the tandem welding joint of 7A52 Al-alloy into account,it is of significance to reveal the effect of the microstructural heterogeneity of the tandem metal inert gas welding joints of 7A52 Al-alloy on the corrosion performance of the micro-arc oxidation (MAO) films prepared on the surface of the weld plate by means of potentiondynamic polarization measurement, OM and SEM with EDS. It follows that the rolling base metal presents a typical fiber-like microstructure. The microstructure of the weld seam is as-cast dendritic structure. Grains in the fusion zone are equiaxed crystallites on the side adjacent to the weld, but are columnar on the other side near the heat-affected zone (HAZ). Recrystallization of grains in the heat affected zone has occurred. The growth rate of the MAO film on the weld seam is slower and Mg can be detected in the film, which may be responsible to the poor compactness and uniformity, and thus the weak passivity of the prepared MAO film, as a result, the protectiveness of the MAO film on the weld seam is worse than that on the HAZ and base metal. In general, for short-term immersion, the difference of the protectiveness of the MAO films on the weld seam, HAZ and base metal is not obvious, however, for long-term immersion, the protectiveness of the MAO film on the weld seam is obviously inferior to that on the HAZ and base metal.