Abstract: The wetting and spreading behavior of SiO₂-BN multiphase ceramics by Ag-21Cu-4.5Ti alloy filler was studied using the base drop method. The microstructure and the formation mechanism of wetting interface were analyzed by SEM and XRD. The relationship among BN content and wetting and spreading behavior was established. The results showed that the typical interface reaction products of Ag-21Cu-4.5Ti/SiO₂-BN were TiN and TiB₂, and the wettability gradually improved with the increasing of BN content in the system. The SiO₂-BN multiphase ceramics were brazed to the Nb. The typical interface structure was SiO₂-BN multiphase ceramics/TiN + TiB₂/Ti₂Cu + (Ag,Cu)/(Ti,Nb)/Nb. The shear strength of the joint first increases and then decreases with the increasing of brazing temperature. When the brazing temperature was 880 ℃ and the holding time was 10min, the shear strength of the brazed joint was 39 MPa.