In this study, a lead-free composite solder was synthesized by adding SnO2 nanoparticles in Sn0.6Cu solder by ultrasonic-assisted method. Effects of the SnO2 nanoparticles on the microstructure, melting property, and the interfacial reaction products of Cu/Sn0.6Cu-XSnO2/Cu brazing joints were investigated. The thickness and grain size of intermetallic compound layer were measured. The results showed that 1.0wt.% SnO2 inhibited the growth of β-Sn in the brazing filler metal and refined the grain size. The melting point of the SnO2-containing solder is substantially the same as that of the SnO2-free solder, but the melting range is significantly reduced. In addition, The application of ultrasonic waves during the solders melting process can refine the grains, the melting point and liquidus temperature of the solder are also lower than the conventional melting solder. the IMC layer at the interface of the solder joint with SnO2 solder is thinner and the grain size is smaller. The main reason is that SnO2 nanoparticles are adsorbed to the crystal plane of the interfacial intermetallic compound, which hinders the interdiffusion between the copper plate and the solder matrix, resulting in a lower driving force for the formation of IMC, thus hindering the growth of interface compound.