Abstract: For a system including several irreversible processes，there are mutual influences between these processes each other. Due to the influence of other spontaneous reactions or processes, some reactions or processes may progress in a direction contrary to their original spontaneous direction. That is called thermodynamic coupling or reaction coupling. In classical point of view the equality of the second law of thermodynamics was always regarded as a necessary and sufficient condition for a system being in equilibrium. However, this assumption (or a premise) is only valid for uncoupling systems. After avoiding this assumption (or premise), thermodynamics has really come into a new era of modern thermodynamics. Modern thermodynamics can be used for any macroscopic system (including very complex living systems). Thus a new field of nonequilibrium nondissipative thermodynamics emerges. The new field still belongs to the equality part of the second law of thermodynamics, so quantitative calculation can be made, and a series of nonequilibrium phase diagrams can be obtained, which agree excellently with a lot of reported experimental data for the activated low pressure diamond syntheses and other new processes.