The laser keyhole welding was carried out onthe butt joints between the Q235 steel sheets with thickness of 3.5 mm and the 6.0 mm thick 5083 aluminum alloy with a fiber laser. The effects of laser distance on the weld shape were investigated. The microstructures and mechanical properties of the joints were investigated by optical microscope, scanning electron microscope,micro-hardness tester and tensile testing machine. Results show that the thickness of intermetallic layer in the interface of the welded joints gradually decreases from 21.0 μm to 4.1 μm with laser distance varies from 0.3 to 0.7mm. When the laser distanceis 0.7 mm and 0.3 mm,the average hardness of the intermetallic layeris 765.4 HV and 671.3 HV, respectively. The maximum tensile strength is 107 MPa when the laser distance is 0.6 mm, which reaches the 80% tensile strength of the 5083 alloys.