Abstract: Distribution of element at the interface in diffusion bonding is a cross behavior related to diffusion, phase transformation, and interfacial reaction, which affects bond performance. Therefore computing technology and numeric simulation were used in order to control diffusion bonding processes and forecast bond quality. In this paper,aiming to make diffusion bonding of dissimilar materials,on the basis of thermodynamic law,the density distribution of element at the interface of the joint was numerically analyzed,and a model of interface reaction for establishing a solid solution interface layer was suggested, so that the effect of diffusion bonding parameters on bond performance can been analyzed qualitatively and semi-quantitatively. Diffusion bonding of heat resistant alloy K5 to heat resistant steel 2Cr12NiMoV validated correctness of this model, and which gave reference to establishing diffusion bonding parameters.