Abstract: Aiming to diffusion bond intermetallic TiAl turbine to steel 40Cr axis, composite isolation diffusion bonding technology was propounded.The isolation effectiveness of the diffusion bonding technology with composite isolation layer was investigated,and the principles of the selecting atomic radius and atomic electronegativity for the layer were found by virtue of the diffusion bondability of materials.In this paper, according to isolation effectiveness principle,intermetallic TiA1 and steel 40Cr are diffusion bonded successfully by using a composite isolation layer Ti/V/Cu.In this case, layers of infinite solid solutions can be found at the V/Cu and Cu/40Cr interfaces which are favorable to the bonding strength, and a diphase Ti3 Al + TiAl layer and a Ti solid solution which enhance the strength of the joint are obtained at the TiAVTI interface.The interface of Ti/V/Cu/40Cr was free from TiC, Ti₃Al+FeAI FeAl 2 intermetallic compounds and other brittle phases, and the strength of the joint was as high as 42OMPa.Isolation effectiveness principle is effective to the selecting of composite isolation layer.