Abstract: Udimet 720 Li is a Ni-based superalloy used for aeroengine disc. Based on the uniaxial tensile, cyclic loading and creep experiments results at 650℃, the Bodner-Partom unified viscoplastic constitutive theory was applied to model the mechanical behaviors of the material under three different loading conditions. After detailed analysis of constitutive characteristics of B-P model, a global optimized strategy for model parameters was given in order to simulate tensile, cyclic and creep curves simultaneously. The B-P model was implemented in ABAQUS soft ware through UMAT subroutine using a self-adaptive time stepping strategy. The results shows that B-P model is able to describe such kinds of mechanical behaviors, but it needs to be modified to model fast isotropic softening and ratchetting.