In this study, intermetallic TiAl and steel 40Cr are diffusion bonded successfully by using a composite barrien layer Ti/V/Cu. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. The reaction products and the interface structures of the joints were investigated by SEM, EPMA and XRD. In this case, a diphase Ti3Al+TiAl layer and a Ti solid solution which enhance the strength of the joint are obtained at the TiAl/Ti interface. Formation mechanism at the interface of TiAl/Ti was propounded. The whole reaction process can be divided into three stages. In the first stage, Ti (ss.Al) layer is formed at the interface TiAl/Ti40Cr. In the second stage, TiAl+ Ti3Al layer are formed adjacent to TiAl, in the mean, the continuous diffusion of Al atoms from TiAl to Ti gives occasion to the formation of Ti3Al. In the last stage, the thickness of each reaction layer increases with bonding time according to a parabolic law. The interface of TiAl/Ti/V/Cu/40Cr was free from intermetallic compounds and other brittle phases, and the strength of the joint was as high as 420MPa, very close to that of the TiAl base. This method gives a reliable bonding of intermetallic TiAl and steel 40Cr.