This study presented a novel fabrication process for TiNi thin films by vacuum diffusion technology using reactive Ni/Ti/Ni multilayer thin films. The sandwiched thin films were prepared by chemical nickel plating. Ni/Ti/Ni multilayer films were heat treated for various diffusion times and temperatures and the influences of the temperature and diffusion time on the interdiffusion behavior of the Ti-Ni system were researched in detail. The results showed that a homogeneous TiNi thin film was obtained at 1173 K with a diffusion time of 4 h. Moreover, the formation sequence of the intermetallics in the Ti-Ni diffusion system was investigated by thermodynamic analysis and experiment. It was found that three compounds -TiNi 3 , Ti 2 Ni, and TiNi -formed in the diffusion process at the Ti/Ni interfaces. More importantly, the nucleation of TiNi 3 and Ti 2 Ni was prior to that of TiNi because of the lower reaction Gibbs free energy and increasing interface energy of TiNi 3 and Ti 2 Ni.