Abstract: The interaction between superconducting thin film of YBa_2Cu_3O_(7_δ) and substrate Of YSZ (Yttric stabilized zirconia) was investigated by AES. It is found after annealing at 900 ℃ that Ba and Cu atoms in the film severely diffuse to and interact with the substrate, white Zr atoms of the substrate do to and with the film, moreover,the diffusion of Ba atoms is more rapid than that of Cu atoms. A thin Ag film deposited on the substrate as a buffer layer seperates the defects on the surface of substrate from the film to suppress the formation of the second phases at the substrate defects as nucleation centre and retard the diffusion of Ba and Cu atoms to the substrate, and lessen the segregation of Cu and CuO in the film.