Three novel Cu–Ni–Al brazing filler alloys with Cu/Ni weight ratio of 4:1 and 2.5–10 wt% Al were developed and characterized, and the wetting of three Cu–Ni–Al alloys on WC–8Co cemented carbide were investigated at 1190–1210 °C by the sessile drop technique. Vacuum brazing of the WC–8Co cemented carbide to SAE1045 steel using the three Cu–Ni–Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5° and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu–Ni–Al/WC–8Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions (such as diffusion and solid solution) of WC–8Co/Cu–Ni–Al/steel system. Compared with the other two brazed joints, the WC–8Co/Cu–19Ni–5Al/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 min, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu–Ni–Al/WC–8Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.