The experiment of the laser overlapped welding for the DP980 and A6061 sheets is conducted and the influences of the nickel foil on the microstructure, the microhardness and the tensile shear property of the weld seam (WS) and the fusion line (FL) of the laser welded joints are compared and analyzed. The results show that, as for the sample without the nickel foil, the entry of the Al element into the weld pool results in the formation of a large number of soft phase δ ferrites and some lath martensites (LM) within the WS and FL. The brittle intermetallic compounds of FeAl2 and FeAl3 separate out near the steel-Al interface, whose peak thickness is about 50 μm, and thus there occur brittle fractures of welded joints at the interface during the tensile process. In contrast, as for the sample with the nickel foil, the nickel element effectively suppresses the Fe-Al metallurgical reaction, and thus the transformation of δ ferrites into austenite is promoted. At room temperature, the WS obtains the full LM microstructure. The WS hardness increases, there occurs the Ni-Al intermetallic compound near the interface, and both the hardness at interface and the thickness of the Fe-Al intermetallic compound layer decrease. The nickel foil makes the laser welded joint strength increase up to 61 MPa, which is 1.4 times that of the sample without the nickel foil.