The TANH material constitutive model accounts for strain softening effect based on the Johnson-Cook (J-C) material constitutive model, which can further reveal the essential properties of the material under the large deformation and high strain rate during the cutting process. In order to verify the accuracy of the method that optimizes the correction coefficient of the TANH material constitutive model, in view of the turning process of the typical difficult-to-machine material Ti6Al4V, based on the TANH material constitutive model, a model for predicting orthogonal cutting forces is established, which considers thermal coupling. The experimental results are in good agreement with the simulation result. In addition, the relationship between the correction coefficient of the TANH material constitutive model and the cutting force is revealed. The input of the force prediction model based on the THAN material constitutive model consist of only the cutting condition, tool geometry parameter and the material's physical parameters. A method for optimizing the selection interval of the correction coefficient of the TANH material constitutive model is proposed. The sensitivity of the cutting force to the correction coefficient in the TANH material constitutive model is analyzed. Then the correction coefficient is optimized and improves the simulation efficiency of cutting force under the premise of ensuring accuracy. The TANH material constitutive model whose correction coefficient is optimized clearly captures the dependence of the strain hardening rate on strain rate. The research results provide theoretical basis for the in-depth study and application of the TANH constitutive model.