Abstract: Dynamic mechanical behaviors of 45 steel have been studied with the split Hopkinson pressure bar(SHPB) and static material test system over a wide range of strain rates and temperatures. The Johnson-Cook constitutive relationship parameters are determined through these experiments. The parameters are validated by comparison between the Taylor experiments and the simulations. The consistency between experimental observation and numerical simulation indicates that the parameters obtained can describe the large strain mechanical behavior of 45 steel under high speed deformation.