Abstract: Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the corrosion resistance of 904L stainless steel welding joints in concentrated sulfuric acid, and the corrosion mechanisms were analyzed in brief. Experimental results show that there are no significant changes in cathodic polarization curves of the weld zone and the substrate, both of them are hydrogen reduction reaction process while an opposite trend is seen upon the anodic polarization curves. Compared with the substrate, the corrosion potential of the wilding zone decreases while the anode current increases. Welding contributes to the anode reaction. The corrosion of the substrate and the weld zone is mainly controlled by the electrochemical step. Both Nyquist graphs are similar, which are composed of a single capacitive reactance arc, having a time constant. The corrosion resistance of the substrate is superior to the weld zone.