The thermal simulation test machine is used to conduct isothermal and constant strain rate thermal compression tests on the thickness of 9Ni steel at the deformation temperature of 770～830℃and the strain rate of 0.1333～0.2667s-1. Through the measured load-displacement curve, the thick plate 9Ni is studied. The stress-strain relationship of steel. The Arrhenius formula of hyperbolic sine form was used to establish a high-temperature constitutive model of thick 9Ni steel, and the correlation coefficient between the predicted real stress and the experimental value of the model was calculated to be 0.969, and the average relative error was 6.18%. The results show that within the range of test temperature and strain rate, DEFORM-3D simulation calculation is carried out using high temperature constitutive equations, and the workpiece has no defects such as cracks and wrinkles, and it is consistent with the actual produced workpiece. Therefore, the high-temperature constitutive model can reasonably predict the high-temperature deformation state of the material, and is suitable for the numerical simulation and analysis of the large-scale head of 9Ni steel thick plate.

　　(1) Using the hyperbolic sine form of the Arrhenius equation, polynomial fitting expresses the material parameters as a function of strain, and constructs a high-temperature constitutive model of thick 9Ni steel.

　　(2) The correlation between the experimental true stress and the model prediction results is R1 and the average relative error AARE are 0.969 and 6.18%, respectively, indicating that the prediction results of the high temperature constitutive model for the thick 9Ni steel established in this paper are consistent with the experimental values. This equation is simple in form, high in accuracy, and easy to obtain. It can be used for numerical simulation and analysis in the forming and processing of large-scale heads of 9Ni steel thick plates.

　　(3) The 9Ni steel high-temperature constitutive model is used for DEFORM-3D simulation calculation, and the workpieces have no process defects such as cracks and wrinkles, which are consistent with the actual production workpieces, indicating that the constitutive equation can better reflect the deformation state of the actual workpiece in the simulation calculation.