Isothermal oxidation behaviors of pure and yttrium-implanted nickel were studied at 900℃ in air. SEM and TEM were used to examine the oxide scales formed on nickel substrate. Acoustic emission (AE) technique was used to monitor the cracking and spalling of oxide film in isothermal oxidizing stage and subsequent air-cooling stage. AE signals were analyzed in time and number domain according to the related oxide fracture model. It was found that Y-implantation greatly lowered the isothermal oxidizing rate of nickel and improve the anti-cracking and anti-spalling properties of NiO oxide film. The main reason for the improvement was that Y-implantation greatly reduced the grain size of NiO and increased the high temperature plasticity and creeping ability of the oxide film. Meanwhile, Y-implantation reduced the size and number of Ni/NiO interfacial defects, hence remarkably enhanced the adhesion of protective NiO oxide scale formed on nickel substrate.