Abstract: The continual development of new concepts and techniques in the field of air traffic management (ATM) generates constantly more diversified demands for an accurate understanding of its underlying structure and operating mechanism. Complexity research, which deals with one of the fundamental issues of ATM, emerges throughout the system at all levels，and provides important clues for exploring the emergence of the ATM system. Complexity science has provided theoretical support for researchers from a methodological perspective in recent years, and numerous papers indicate that the subject is now a hot topic in ATM. However, there is as yet no widely accepted architecture for ATM complexity research up to now. Therefore，this article analyzes the mainline and framework of previous work，focusing on existing achievements in dynamical density, traffic disorder, flow disturbance analysis and airspace complex system modeling. It also points out the future research and development trends in the field of ATM complexity and some key issues which remain to be solved.

Key words: air traffic management, complexity, dynamical density, disorder, flow disturbance analysis, complex system modeling