Abstract: Si3N4 ceramic and 40CrMo steel was brazed in vacuum using AgCuTiPd active filler alloys with different Pd content.Microstructure and properties of the joint were investigated.The results show that titanium in the filler alloy react with Si3N4 ceramic and 40CrMo steel,resulting in the formation of TiN＋Ti5Si3 and Fe-Ti compound reaction layers at ceramic/filler and steel/filler interfaces,respectively.With increasing palladium content (atom content)in the filler alloy from 5% to 20 %,thickness of the reaction layer and distribution of reactants in the joint change and strength of the joint increase when the Pd content is lower than 10 and then decreased when the Pd content is higher than 10%.