Abstract: The 5 mm thick 304 stainless steel plates were lap joined by using vacuum brazing with Cu-23.5 Mn-xNi(x=9.1, 9.4, 9.7, 10) copper-based brazing filler metals, and the effect of Ni content of the brazing filler metal on the microstructure and mechanical properties of the brazing seam was mainly studied. The results show that good metallurgical bonding between the CuMnNi brazing filler metal and the base metal at both sides is formed, and the microstructure of the brazed joints is dense without obvious defects such as cracks and holes. The higher the Ni content, the more the Ni content enriched at both sides of the brazing joint, and the less the Ni content in the brazing seam, the lower the shear strength of the brazing joint. When the Ni content of the brazing filler metal is 9.1%, the brazing temperature is 970 ℃, and the holding time is 15 min, the brazing joint with the best performance can be obtained, and the maximum shear strength of the joint at room temperature is 159 MPa.