Abstract: In this paper, unified elastic-viscosic-plastic theory which can compute the change of elastic, viscosic and plastic situation of each point in the body is suggested. The theory is based on the laws of thermodynamics and the pseudo elastic postulate. In the paper, the constitutive equations and variational principles are deduced. From which the finite element method of both space and time may be esily formulated. Note that, by choosing the material parameters properly, the plastic constitutive equations currently used may be given.