During the fracture splitting process of the connecting rod, the plastic deformation, especially the plastic deformation before cracking, not only causes the big end hole of the connecting rod to be out of roundness, but also increases the residual stress, affecting the assembly precision and even the service life of the connecting rod. In this paper, the mechanical properties of microalloyed steel C70S6, 36MnVS4 and 46MnVS5 connecting rod were determined by tensile test. The displacement field, plastic strain and the deformation principle of the big end before the crack initiation of the fracture splitting of the connecting rod were numerically simulated. The results show that the yield strength, tensile strength and plasticity index of the new medium carbon microalloyed steels 46MnVS5 and 36MnVS4 are significantly higher than those of C70S6. However, the C70S6 connecting rod has a long loading time before crack initiation, and the plastic deformation area of the groove root front is large and the strain is high. The plastic deformation of 36MnVS4 and 46MnVS5 connecting rods is small and the area is concentrated. Among the three, the 46MnVS5 connecting rod has the smallest deformation and the C70S6 connecting rod has the largest deformation.