Abstract: In order to investigate the microstructure and properties of laser-welded joints of 2.2 mm new ultra-high-strength steel, the laser butt welding was employed, combined with finite element simulation to design two sets of welding process parameter schemes: High power-high speed and low power-low speed. Under the optimized process conditions, the macro morphology, mechanical properties, and microstructure of the welded joints were systematically analyzed. Through mechanical performance testing and microstructural analysis, key data such as tensile strength, elongation, and hardness of the welded joints were obtained. The results indicate that when the laser power and welding speed are 1000 W, 10 mm/s and 2000 W, 22.5 mm/s respectively, the welded joints achieved full penetration, with tensile strengths of 80% and above 90% of the base material, respectively, and elongation rates both reaching 14%. The hardness distribution exhibited an M-shape, with the hardness of the weld metal zone significantly higher than that of the base material, while the heat-affected zone experienced significant softening. The reduction in the mechanical properties of the welded joints was primarily attributed to the non-uniformity of the microstructure, and the hardness differences in the welded joints were mainly caused by phase transformation. This study provides a solid theoretical foundation and practical guidance for laser welding technology in the field of ultra-high strength steel.