To obtain excellent welding joint, ultra-high strength steel 30CrMnSiNi2A was welded by laser. Microstructure, properties, tensile strength, tensile fracture and residual stress were investigated by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing machine,electronic universal testing machine and X-ray stress analyzer. The experimental results indicate that microstructure of central welding zone, near central zone and edge zone is equiaxed crystal, dendrite crystal and rough cylindrical crystal, respectively. Microstructure of fusion zone is fine cylindrical and equiaxed crystal. Microstructure of heat-affect zone (HAZ) is mainly lath martensite, bainite and residual austenite. The phases of welding zone is mainly comprised of α-Fe, NiCrFe, Fe-Ni and MnSi2.The highest hardness value of welding zone is 518 HV, the highest value hardness of HAZ is 560 HV. The hardness decreases significantly from HAZ to substrate. The average tensile strength of welding joints is approximately 802 MPa. The fracture appears in substrate near welding zone. The impact toughness of weld joints is 75.7 J/cm2. The residual stress of welded joints is the compressive stress. The average residual stress of weld zone is -17 MPa, and average residual stress of HAZ is -59 MPa.