Abstract: The atmospheric corrosion characteristics of the weld zone of storage tank steel Q345R are studied, and the corrosion behaviors of the heat affected zone, weld and base metal are analyzed by polarization curve and AC impedance technique. The surface corrosion microstructure and compositions of the samples are characterized by scanning electron microscope and laser Raman spectrometer. The results show that the base metal has the greatest corrosion susceptibility, and the weld zone is more resistant to corrosion than the heat-affected zone. There is some relationship between the corrosion tendency and the microstructure. The microstructure of the weld zone consists of granular bainite and acicular ferrite, and the refinement of the microstructure of this zone can obviously reduce its corrosion susceptibility. The welding process makes the weld almost a non-porous area; therefore, the base metal with micropores has a higher corrosion rate.