Abstract: Butt welding was carried out on the T-joint of SMA490BW/Q345E dissimilar steels by CO₂ shielded arc welding, and then the joint was annealed at 590 ℃ for 3 h. The microstructures, hardnesses and corrosion resistance before and after annealing were compared. The results show that before and after annealing, the weld interface was obvious in the joint, and the microstructures of the weld consisted of proeutectoid strip ferrite, pearlite and granular bainite. Before annealing, from surface to inner, the microstructure of the weld changed from coarse columnar grains to alternating columnar grains and equiaxed grains, and the hardness difference was large. After annealing, the microstructures of different layers had little difference, and the hardness distribution became uniform. The corrosion tendency of the annealed weld was reduced and the corrosion resistance was improved. During wet/dry cyclic exposure in NaCl solution, pitting corrosion occurred on the surface of non-annealed and annealed weld and the rust layer cracked in the latter stage of corrosion (100 h). The rust layer was denser after annealing.