Abstract: Conceptions of similarly non - coupled systems and equations are introduced. On the basis of the similarly non-coupled equations, two theorems of different work of similarly non-coupled systems for deformation theory and flow theory are derived. In terms of the two theorems, simulated potential energy principles and simulated complementary energy principles of similarly non - coupled systems for deformation theory and flow theory in plasticity are established. The applications of the simulated potential energy principles for deformation theory and flow theory are given.

Key words: Plasticity, Similarly non-coupled equations, Simulated variational principle