The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000℃ in air by thermal-gravimetric analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the morphology and structure of the oxide film after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the stress changes within oxide films. It was found that lanthanum implantation remarkably reduces the isothermal oxidizing rate of Co-40Cr and improves the anti-cracking and anti-spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduces the grain size and internal stress of Cr2O3 oxide and increases the high temperature plasticity of oxide film. Lanthanum mainly exists in the outer surface of Cr2O3 oxide film in the forms of fine La2O3 and LaCrO3 spinel particles.