Abstract: 52CrNiMoVSi hot-working die cracked abnormally during hot-forging operation, and the cracking is located at the bottom of the working surface. The cracking parts are cut and sampled, and the causes of cracking are analyzed and discussed through macroscopic and microscopic observation of the fracture, metallographic observation, hardness test, and energy spectrum analysis. The results show that the 52CrNiMoVSi hot-working die cracked in the form of fatigue fracture. Because the matrix contains many non-metallic inclusions, the purity is low, the composition and structure are not uniform, resulting in uneven hardness and reducing the fatigue strength of the material. In the continuous working of the mold, the radius of the cavity fillet of the hot work die is too small to cause large stress concentration, which leads to crack initiation and propagation, and eventually leads to abnormal cracking, which makes its life much lower than the life of normal parts.