To research the tailor welding of cold rolled multi-phase steel and high strength low alloy (HSLA), tailor welding is conducted with 10 kW fiber laser varying laser power, welding velocity and defocusing amount. Weld seam formation, metallographic microstructure, hardness and formability are tested. The results show that the formation of weld seam is sound. The metallographic microstructure of weld seam is mainly lath martensite dendrites. Heat affected zone of multi-phase steel is combined with tempered softening zone, fine grain equiaxed zone, coarse grain equiaxed zone and the mixture zone. The width of softening zone is affected by welding velocity most severely. The tensile strength and formability of weld seam are sound. The fracture location of tensile specimen is base metal of HSLA consistently. The fracture location of Erickson LDH test is parallel with the weld seam on the side of HSLA. The results can provide guidance on welding processing and theory of tailor welding of multigauge cold rolled multi-phase steel and HSLA.