Abstract: Welding metallurgy is characterized by extreme conditions including high temperature, transience, and non-equilibrium, making it difficult for traditional post-mortem characterization methods to capture the true trajectory of its transient evolution. The high-temperature confocal scanning laser microscope (HT-CSLM) overcomes the static limitations of conventional welding metallurgy research and pioneers the in-situ, dynamic observation of microstructure evolution during welding thermal processes. Herein, starting from the working principles of this technology, the cutting-edge achievements obtained using HT-CSLM in the areas of weld pool solidification, solid-state phase transformation and defect formation are reviewed and summarized. Special emphasis is placed on elucidating the unique advantages and prospective value of HT-CSLM in addressing specific concerns in welding metallurgy. Finally, future development directions are proposed, including expanding the range of material systems studied, integrating with additive manufacturing, correlating with mechanical properties and advancing online monitoring techniques.