In the dynamic and multi-task condition of air traffic control, an Air Traffic Controller (ATCO) is required to construct effective control strategies to handle multiple aircraft simultaneously. Effective strategies can prevent potential collision of aircraft well in advance and can contribute to reduce ATCO's cognitive workload. Therefore, the strategy building skill is quite important for ATCOs in order to realize safe and efficient air traffic flows. However, it is sometimes difficult to transfer this kind of cognitive and situation-dependent skill from ATC training instructors to trainees with conventional education and training methods. In the present research, a supportive function of education for an ATCO trainee which can visualize the difference of task performance resulted from the variety of possible control strategies has been proposed. The supportive function has been implemented using the framework of a cognitive system simulation of ATCO termed "COgnitive system Model for simulating Prediction-based behaviors of Air traffic controller in dynamic Situations (COMPAS)". Using this function, the effect of ATCO's control on air traffic flow has been successfully visualized, which helps trainee to understand the differences of the consequences of the different strategy. This result has strongly implied that the COMPAS equipped with performance visualization function can be utilized as a supporting tool for education of ATCO trainees.