Abstract：Rapid development of process industries has caused the severe environmental pollutions. Implementing cleaner processes that use or generate lower amounts of or less harmful pollutants will require systematic methodology of green process synthesis and design based on the principles of green chemistry. The current widely used environmental performance assessment criteria and methodologies are introduced and analyzed in this paper. The modeling and algorithms for green process synthesis and optimization design have been reviewed. Then, the principles, methods and developing trend of green process design are discussed and highlighted with two industrial cases. Combining the green chemistry with the methodology of process system engineering, we propose the green degree theory and methodology, and define the relevant research contents and application perspective. The basic methodologies of evaluating quantitatively the green degrees of material, energy, process and eco-system are established. Then, the green system integration procedures would be carried out with multi-objective optimization methodology and decision making strategy to reach the global sustainability of ecological, economic and social areas.