Abstract: This paper proposed that stress may be expressed as a functional of the intrinsic geometry parameters of plastic strain space. In general, the plastic strain space is not an Euclidean geometric space and its measure tensor is a function of not only coordinates (plastic strain) but also plastic strain history. However, it can be taken as an Euclidean one for the case when the material is initial isotropic and plastically incompressible. Based on the theories of Ilyushin and Valanis, a new integral elasto pl...