2198 aluminium-lithium alloy is extensively used in the field of aerospace due to the favorable properties, such as low density, good mechanical property, high specific strength, good thermostability and plasticity. 2198 aluminium-lithium alloy is welded by fiber laser using the filler of ER4047 Al-Si. The microstructure and corrosion behavior of joint in NaCl solution with 3.5% mass fraction is studied. The micromorphologies, precipitate species and their distribution have been examined using the optical micrograph, scanning electron microscope and transmission electron microscope. The corrosion behavior of weld and base metal has been compared by the methods of immersion test and electrochemical corrosion test at room temperature. The results indicate that the microstructure of 2198 aluminium-lithium alloy base metal, compared to the weld, is coarser and grows along to the rolling direction. Plenty of T1 precipitates with the diameter of hundreds of nanometers distributed randomly in the base metal. After laser welded with the filler ER4047 Al- Si, the heat affected zone is narrow, the microstructure is tiny, the component is uniform, the kind of precipitate is various, and the fine grain is equiaxed, the columnar crystal is vertical growth close to fusion line. At room temperature in NaCl solution with 3.5% mass fraction, the weld and heat affected zone show the uniform corrosion behavior, the small corrosion spot area, the shallow corrosion spot. By comparison, the parent metal shows the pitting corrosion. With the immersion time increasing, the pitting area is enlarged and the depth is deeper. The open circuit potential, self-corrosion potential and polarization resistance of weld are all higher than those of the parent metal, but the corrosion current density is less than that of the parent metal.