The simulation precision of metal plasticity is closelyrelated to yield criteria and constitutive law which are used incomputational model. In order to improve this precision under complex stressstate, tensile tests with five kinds of samples, such as smoothround bar, round bar with small notch, round bar with large notch, thinplate with central hole and thick plate with central hole, were conducted.Parallel finite element models were built for each test and solved inABAQUS. In these simulations, von Mises yield criterion, Tresca criterion,Twin-Shear criterion were separately used based on equivalent stress-straincurve as the constitutive law. The results showed that none of them had asatisfying precision for all these different tests. So Von Mises criterionwith stress triaxiality dependence was used as yield function. Tangentmodulus with principal stresses correction based on equivalent stress-straincurve was used as elasto-plastic constitutive law. With this theory, theabove tests were recomputed. The results further showed that, comparing withother criterions, von Mises criterion with stress triaxiality correction hasa better precision than other yield functions. The tangent modulus withprincipal stresses correction which is first postulated in this paper has abetter estimation of 2A12-T4 Aluminum Alloy's Elasto-plastic behavior thanthe assumption with unique equivalent stress-strain curve.