In order to research the influence of laser power on the welding of steelaluminum dissimilar materials, the overlap welding experiments of dissimilar materials for high strength steel DP780 and aluminum alloy 5052 with thickness of 2 mm were carried out by using fiber laser. Highspeed camera, universal stretcher, metallographic microscope and scanning electron microscope were used to carry out experiments. The images of welding process, tensile strength of joints and crosssection of welds were obtained. The effects of laser power on the spatter, mechanical properties and crosssection morphology of the welds were studied. The results show that when the welding power is 2.3 kW, the welding process is the most stable; when the welding power is 2.5 kW, the tensile strength of the weld reaches the maximum value of 35.63 MPa. When the laser power is too high, too many intermetallic compounds are formed at the interface, and the welding process is too unstable. It has a negative impact on the tensile strength of the weldment. When the laser power is suitable, the joints with good mechanical properties can be obtained.