Synthesis or creation of a new, process system may be one of the most attractive work for engineers. At present we are requested to propose new, systems to develop a sustainable society and to keep the globe clean. For creation of ideas, some jump mechanism in brain is required, since there is no explicit algorithm for it, The contents of this paper are based on my experiences. First. the basic mechanism of human brain is discussed. Then three phases of process system synthesis are discussed in analogs to the architectural design of our own house. New thermodynamic approaches are developed for these three phases of design.