Abstract： The hot deformation behavior of a EH40 ship plate steel was studied by a ThermecmastorZ simulator in the temperature range of 850-1050℃ at strain rates of 0005-10s-1. The hot deformation equation of the steel was determined and the processing map based on the dynamic material model(DMM) was also established. The results show that the predicted value of deformation resistance model of EH40 ship plate steel is in good agreement with the measured data, the activation energy of EH40 ship plate steel for hot deformation is 324.479kJ/mol, the optimum processing window for hot deformation of EH40 ship plate steel is identified as 850-1050℃, strain rate less than 10s-1and strain not higher than 04 when dynamic recrystallization easily happened.