Abstract: The welding performance of steel structures such as offshore platforms, ships, bridges, buildings, and oil and gas pipelines directly determines the service life and safety of the structure, the importance of which cannot be minimized. In welding-related research, the toughness of the welding heat-affected zone is a key issue. This zone experiences temperatures as high as 1400℃, thereby causing the formation of coarse austenite grains. If the welding parameters are improperly controlled, microstructure refinement cannot be achieved by subsequent phase transformation, which results in decreased impact toughness. Multi-pass welding is even more complex, with the secondary heat input affecting the coarse-grain zone formed during the previous pass. This results in the formation of necklace-type M-A constituents, which also lead to deterioration in toughness. In this paper, the relevant research results were summarized with regarding the welding heat-affected zone and it was discuss that the composition of the parent material, the second phase, the welding process, and other factors effect the microstructures and properties of the heat-affected zone. This paper also offers ideas for improving the welding performance of large steel structures in low-temperature service circumstances.