Abstract: In order to make up the insufficient research of the dynamic mechanical properties and dynamic constitutive model of 18CrNiMo7-6 alloy steel, using MTS servo fatigue testing machine, tensile test system at high temperature based on DIC and split Hopkinson pressure bar (SHPB), the stress-strain curves at different strain rates and temperatures were obtained.The results show that 8CrNiMo7-6 alloy steel has obvious strain rate strengthening effect and temperature rise softening properties.The Johnson-Cook (J-C) constitutive model was used to describe the dynamic mechanical properties of 18CrNiMo7-6 alloy steel.The J-C constitutive model parameters were determined by the experimental datas, and then the reliability of the parameters was verified by the numerical simulation of SHPB test.The strain hardening term and strain rate strengthening term were modified in the J-C constitutive model.The modified J-C constitutive model is in agreement with the experimental datas, which can provide a reference for numerical simulation in practical engineering.