Aiming at the high difficulty of quantifying the complexity of terminal airspace operational situations and the limitation of evaluation dimensions, a method for assessing air traffic complexity, which is based on network interdependence, has been proposed in this paper. It is done according to the relationships of relative motion and the dependencies of air traffic control coordination. Taking into account the conflicts between interlayer nodes of the control and flight networks, as well as the correlations among interlayer nodes, a control-flight interdependent network and an air traffic network complexity model have been established. The Pearson correlation coefficient is used to analyze the factors that influence network complexity, identifying the critical nodes that have a significant impact on network complexity. It also verifies the correlation between node flight parameters and network complexity. Finally, the key factors affecting traffic complexity are identified and validated from the perspective of regulation deployment. The evaluation model has been validated using historical ADS-B data from Beijing Terminal, showing that the complexity assessment method that considers network interdependence provides objective and timely indications of complex air traffic situations with enhanced predictability. It is found that network complexity is highly correlated with the complex state of critical flight nodes, and the rate of change in node speed is a key factor affecting network complexity. The speed intervention of critical nodes can control the development of network complexity to a certain extent, thus ensuring the safety of air traffic operations.