Abstract: In order to improve the quality of dissimilar steel welding. Adopting laser welding technology welding of two heterogeneous materials, Q345B low alloy steel, and the 304 stainless steel. Under different laser powers, the welded joints were thoroughly characterized and analyzed using metallographic microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Experimental data indicates that when the laser power is higher than 3 kW, the joint can be fully welded, and the weld sections of 4 kW, 4.5 kW and, 5 kW all present the waist phenomenon. The weld microstructure is typical lath martensite. The size of the lath martensite in the weld of 5 kW is smaller, showing the highest hardness value. The tensile strength of the weldment of 4 kW reaches 590 MPa. With the increase of laser power, the tensile strength of the weldment gradually decreases. In the weld, there are no M₂₃C₆ and σ phases, which have a great influence on the quality, but mainly Cr₂Ni₃, Fe₂Ni₃, and α-Fe phases. The results indicate that using laser wire filling welding technology can achieve high-quality welding of Q345B/304 dissimilar steel.