Abstract: Objective 904L stainless steel is welded by ultrasonic-assisted laser welding to solve the problem of segregation and porosity in laser welding of 904L with high alloying degree. Methods The microstructure, properties and segregation behavior of crystal elements in molten pool of welded joints under different welding processes are discussed. Results Compared with conventional laser welded joints, the grains in the weld zone of ultrasonic-assisted welded joints change from coarse dendrites to fine equiaxed grains, and width of fusion zone decreases. Tensile samples of welded joints are broken in the weld zone, tensile strength does not change significantly, and impact performance is improved by 26.4%. Impedance modulus of welded joints increased by 9.24%. Conclusion The comprehensive performance of welded joints is improved greatly.