Abstract: The 4 mm thick Mg-Al-Zn alloy plate is welded by using laser beam welding (LBW) and laser beam welding with filler wire (LBW-F), respectively. The corrosion mechanism of the Mg-Al-Zn alloy joint is discussed. Some technical means involving polarization curve measurement, electrochemical impedance spectroscopy test, scanning electron microscopy (SEM) observation and energy dispersive spectroscopy (EDS) analysis are employed. The corrosion behavior of the LBW and LBW-F joints in the 3.5%NaCl aqueous solution is investigated, and is compared with that of the base metal (BM). Results show that the corrosion product is mainly composed of Mg(OH)₂ and carbonate, and that the corrosion resistance relationship of the joints and BM can be expressed as LBW joint >LBW-F joint >BM.