Abstract: Living system is a non-equilibrium open system having the function of self-organization and self-control. The study of energy principle of living system involves two principal parts: mechanics and thermodynamics. The classical infinitesimal deformation theory and thermodynamics of equilibrium state are not sufficient to explain the complex motion of living system. We aim in this paper to describe the mechanical energy principle of macroscopic motion of living body based on large deformation non-symmetry stress field theory. The principle of irreversible thermodynamics applied to livihg system will be left in another paper^[9].

Key words: living system, energy principle, large deformation, S-R decomposition theorem, biomechanics