Abstract: Prefabricated cracks were made on GCr15 bearing steel by grooving. When the temperature was 500-1 150 ℃, the crack heating oxidation was simulated, and the decarburization and oxidation mechanism of the heating process were analyzed and discussed. The results show that the decarburization of GCr15 bearing steel could occur at 850 ℃ for 10 min under normal oxidation atmosphere. With the increase of heating temperature, the depth of decarburization layer was deeper. When heated at 800 ℃ for 10 min, obvious oxide layer began to appear. With the increase of heating temperature, the oxide layer at the crack was thicker. After heating at 1 100 ℃ for 10 min, obvious oxide dots began to appear in the steel matrix on both sides of the crack. The higher the temperature, the larger the particle size and density of the oxide dots. The oxide dots near the crack could not be used as the basis for judging the nature of the defect, but could only be used as the basis for judging whether the crack was generated at high temperature or medium and low temperature.