Abstract: The Ag-Cu-Zn brazing filler metal containing 21wt% Ag was microalloyed with Sn, P, Ni and In, and the melting performance, spreading performance and processing property for brazing filler metal, and the tensile strength and microstructure of the brazed red copper and 45 steel joint were studied.The results show that the optimum composition (mass fraction/%)of microalloyed Ag-Cu-Zn brazing filler metal was 21Ag-Cu-Zn-1.5Sn-0.2P-1.0Ni-2.5In.Compared with 21Ag-Cu-Zn-1.5Sn quaternary alloy brazing filler metal obtained by prior optimization, the solidus and liquidus temperatures decreased by 106 ℃ and 31 ℃, respectively, the spreading area per mass on red copper base metal increased by nearly 66%, and welding wire with diameter of 0.8 mm could be made by conventional hot extrusion and drawing.When the brazing filter metal was used for brazing red copper or 45 steel, a dense and defect-free brazing joint formed with a metallurgical bonding layer at the interface; compared with 21Ag-Cu-Zn-1.5Sn brazing filler metal, the tensile strength of the joint for brazing 45 steel increased by about 11%.