Abstract: It has been more than twenty years since the energy cascading utilization principle and the concept of total energy system were proposed by professor WU Zhonghua. Thanks to this guidance the innovations of the energy and power system have made a great advancement. The recent progresses and breakthroughs in the theory of total energy system are reviewed in this paper, including the expansion of energy utilization from the field of physical energy to the field of chemical energy and further the combined cascade utilization of physical and chemical energy; the methodology of total energy system analysis based the energy level change of related processes; the thoughts and innovations of system integration such as system of coupling chemical production and power. Total energy system has been an important branch of energy science and makes more and more contribution to the sustainable development of scientific energy utilization, economy and society.

Key words: System integration, Thermal cycle, Total energy system