Since the concept of complexity science was introduced into the field of air traffic management (ATM), a large number of scholars have conducted related complexity research. However, the researchers have long been anxious to define the complexity which is still vague and difficult to unify. But there is a lack of systematic research on the complex traffic formation mechanism in the field of ATM. If typical traffic phenomena could be comprehensively analyzed and the formation cause of complex situation of the air traffic could be clarified, then the study on the complexity in the field of ATM will gain great benefit. Therefore, models are built by choosing three traffic phenomena such as queuing, flight conflict avoidance and asymmetric situation information distribution. Then the paper analyzes the mechanism of the formation of complex traffic situation, mines the impact factor of the complex traffic situation, aiming at the common law of forming a complex traffic situation so as to further study the complexity of the air traffic management.