This chapter systematically elaborates on the exergy analysis method for thermodynamic processes, centering on the concept of exergy which defined as the maximum capacity of energy to reversibly convert into useful work under specific environmental conditions. It categorizes exergy (e.g., thermal exergy, mechanical exergy, chemical exergy) and details calculation methods, emphasizing that exergy loss arises from irreversible processes degrading energy quality. Exergy balance equations quantify such losses, while exergy efficiency contrasts with thermal efficiency, highlighting its superior reflection of energy conversion quality. The chapter introduces energy level analysis to evaluate energy quality alignment and applies exergy principles to case studies (e.g., turbines, heat exchangers), underscoring energy optimization through minimizing irreversible exergy losses.