Based on the experimental data of true stress-strain measured by DIC (Digital Image Correlation) combined with the data from a tensile test machine, the methodology for establishing a constitutive model for Ti40 alloy sheet is presented in this paper. The procedure is demonstrated by building the constitutive relationship for Ti40 alloy sheet. As the verification of the constitutive relationship, a force-displacement diagram is simulated by FEA (Finite Element Analysis). A comparison of force-displacement diagram obtained separately by FEA and the tensile test machine is made and the result shows that the method for establishing the constitutive relationship for Ti40 alloy sheet presented in this paper are reliable and considerately accurate. As a material constitutive model, the establishment of constitutive relationship of Ti40 alloy sheet will effectively provide the experimental validation for FEA in activities of the high accurate non-linear numerical simulation for sheet-metal manufacturing of structural parts with complicated geometry.