Abstract: The corrosion behavior of flux residue was studied systematically by means of scanning electron microscope and electrochemical workstation. The results showed that both the brazing filler metal and the matrix corroded in the aqueous solution of flux, and the corrosion rate of the matrix was obviously higher than the brazing filler metal. The corrosion rate decreased with time, but not stopping. The finer the solder structure was, the more corrosion reactions will occured in the atoms with irregular arrangement at grain boundary, and the corrosion resistance would decrease. There were microscopic cracks between the zinc layer and Fe matrix of bundy tube, and strong corrosive substances in the brazing agent had penetrated into the interface layer. In the zinc-coated region, a large amount of zinc element was oxidized to form ZnO. In the region of residual brazing agent layer, Fe and Zn elements with high content and poor corrosion resistance had diffused into the region of residual brazing agent layer to form iron oxides, and some of them react with NaCl to form FeCl3 and other substances.Highlights: The corrosion behavior of the flux residue was investigated and its influence on the reliability of the brazing joint was determined.