Abstract: The influencing factors of fracture bluing effect of 42CrMo4 steel were analyzed by means of experimental studying the microstructure, specimen placement and heat treatment process of the material. The results show that when the original structure of the fracture material was fine and uniform, the fracture surface of the sample was placed toward the furnace door, the heating temperature was 390 ℃, and the holding time was 40 min, the bluing effect of the fracture was the best, and the white thin strip or granular inclusions on the fracture surface appeared obviously.