Abstract: The isothermal spheroidizing annealing effect with different temperatures and cooling rates was investigated by SEM analysis and hardness test, and the morphology and distribution of the carbide under different process parameters were analyzed by quantitative metallography methods. The results show that the hardness distribution was most uniform and the spheroidizing annealing effect was best when the GCr15 bearing steel was austenitized at 790 ℃ and cooling at 20 ℃·h-1. In this case, the standard deviation about average particle diameter of carbide was the minimum, the ratio of the major axis and minor axis was not greater than 2.1, the particle roundness was not less than 0.17, and percentage of 0.5~1.1 μｍ carbide was about 50%. This method can provide some references to accurately and quantitatively evaluate the spheroidizing annealing effect of GCr15 bearing steel, and it is significant for practical production.