The double-vacuum smelting medium alloy Cr and Mo bearing steel was used as experimental material to study the microstructure and room temperature rotating bending fatigue performance after ion nitriding.Experimental The results of Experimental show:The medium alloy Cr and Mo bearing steel is tempered sorbite after being processed (930°C+550°C). The compound layer in the nitriding layer isγ′phase (Fe4N) and CrN, and the thickness is about 16 μm, which is not conducive to matrix fatigue performance improvement.The fatigue limit of the 32Cr3MoVE bearing steel after nitriding is 947 MPa, which is 19.4% higher than the fatigue limit of the unnitrided sample. The stress distribution is in the four-level stress gradient, and the cracking methods mainly include the cracking of the surface compound layer and the cracking of the non-metallic inclusions on the subsurface. At the same time, the surface roughness and nitriding compound layer have great influence on the fatigue life of nitrided samples.