Si3N4 and 40CrMo steel was joined using Ag-Cu-Ti-Pd brazing filler. Microstructure of the joint and bonding interface was studied by SEM and EDS, and the phase structure was analyzed by XRD. The results indicate that reaction layers at ceramic/ filler alloy and filler alloy/steel interfaces are formed. There is a reaction layer containing TiN and Ti5Si3 between ceramic and filler alloy, while the reaction layer between filler alloy and steel is composed of Fe-Ti compound. The middle part of the joint is an eutectic structure composed of Ag-riched and Cu-riched solid solutions. With the increase of the brazing temperature, the thickness of the joint seem decrease, the thickness of the reaction layer between Si3N4 and filler alloy increases and then decreases, and the thickness of the reaction layer between filler alloy and steel increases.