Abstract: To evaluate the microstructural evolution and service performance of laser tailor-welded joints in thin Al-Si-coated hot stamping steel, equal-thickness and equal-strength joints of 1 500 MPa-grade hot stamping steel, as well as dissimilar-thickness and dissimilar-strength joints of 1 000 MPa-grade/1 500 MPa-grade hot stamping steels, were investigated. The results show that the thin coating with a thickness of approximately 12 μm effectively reduces the dilution of Al into the weld, maintaining the Al content in the weld at 0.2% ~ 0.3% (mass fraction). After holding at 930 ℃, the weld is fully austenitized and subsequently transforms into martensite during rapid cooling. For the equal-thickness and equal-strength joints of 1 500 MPa-grade hot stamping steel, the hardness of both the weld and the base metal after hot stamping is approximately 480 HV, and the tensile strength reaches 1 474 ~ 1 493 MPa. Fracture occurs in the base metal in all cases, indicating that no obvious weld softening occurs. In the directly welded joints of 1 000 MPa-grade/1 500 MPa-grade hot stamping steels, the hardness near the weld boundary on the 1 500 MPa-grade steel side decreases to 458 HV ± 6 HV because the C content in this region is lower than that of its base metal. Consequently, the strain concentrates in the weld, leading to joint fracture at below 1 400 MPa. After filler welding with a 0.7% C wire, the C content at the weld boundary is compensated, and the hardness increases to 486 HV ± 4 HV. The low-hardness zone is eliminated; fracture shifts to the 1 500 MPa-grade steel base metal, and the load-bearing capacity and reliability of the joint are significantly improved.