Abstract: The microstructure and mechanical properties of 25Cr3Mo guide shoe steel after failure were studied. The microstructure of 25Cr3Mo steel was observed and analyzed through metallographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The tensile strength, impact toughness, and micro-nano mechanical properties were tested. Combined with the results of Ansys numerical simulation, the failure reason of 25Cr3Mo guide shoe steel was obtained. The inclusion of particles of S、Cr、Mn and Mo elements in the material results in instability of the material structure and mechanical properties. The internal defect areas of the material exhibit significant stress concentration in the geometric transition area of the component during external loading, and the defects serve as the nucleation site of the crack to promote crack initiation and accelerate the crack propagation process.