Abstract: For SM490A steel and SUS304 steel samples with I type cracks, the mechanical characteristics of cracks tip and plastic deformation regions were analyzed by measuring the acoustic emission characteristic parameters and the temperatures at the specific points of crack tips during tensile fracture. The results show that the acoustic emission energy count and ring cumulative count have obvious curve characteristics in each stage of crack growth, and the curve characteristics are basically consistent with the stress-strain curves of yield and strengthening stages. Therefore, the acoustic emission energy count and ring cumulative count can be used to describe the plastic deformation at the yield and strengthening stages. The temperature change of sample from deformation to fracture be determined by plastic deformation rate. For SM490A steel and SUS304 steel with I type cracks, the acoustic emission signals mainly focus on the plastic deformation stage and crack growth stage.