Abstract: This paper systematically restructures the teaching system for plasticity constitutive theories. The entire logic revolves around mechanical equilibrium, which is a fundamental concept in classical mechanics. We first clarify that the yield function is essentially an equilibrium constraint. Then we derive both rate-independent and rate-dependent plasticity theories in a unified way. The framework covers three main types, i.e., rate-independent elastoplasticity, classical elasto-viscoplasticity, and unified viscoplasticity. We also design a progressive, inquiry-oriented teaching system. Its main modules include comparative analysis of governing equations, parametric studies on rate sensitivity, and expanded discussions on non-equilibrium plastic responses. The teaching process forms a closed loop. It starts from basic physical interpretations, moves on to practical engineering applications, and finally extends to research frontiers such as nonlocal plasticity. This arrangement helps students clearly see the physical meaning, internal connections, and applicable conditions of each model. Overall, this proposed system offers a practical way to reform plasticity mechanics courses by rebuilding the underlying physical principles.