Air traffic flow management(ATFM) is a collaborative process between the airspace provider and the airspace users. The result of the collaboration should be an outcome that maximizes the utility of the system without excessively penalizing any of the agents. This paper develops a discrete-event simulation model which consists of aggregate departure/arrival airports, flight routes, and sectors for evaluating the alternative collaborative route selection strategy. Given the different perspectives from air traffic control center(ACC) and airlines, eight performancemetrics and five alternative route selection strategies represent the past, current and proposed air traffic flow management operations that were evaluated. The Monte Carlo method combined with the Optimal Computing Budget Allocation(OCBA) simulation optimization technique is employed to assess the performance of different strategies. A case study of the upper air routes in central and southern China shows that the proposed model can be readily implemented to simulate different kinds of air traffic flow management strategies and predict the effect of changes on the airspace system. It also shows that the proposed alternative collaborative route selection strategy is an effective way in alleviating the en-route traffic congestion. The result of the collaboration should be an outcome that maximizes the utility of the system without excessively penalizing any of the agents. This paper develops a discrete- event simulation model which consists of aggregate departure / arrival airports, flight routes, and sectors for evaluating the alternative collaborative route selection strategy. Given the different perspectives from air traffic control center (ACC) and airlines, eight performance metrics and five alternative route selection strategies representations the past, current and proposed air traffic flow management operations that were evaluated. The Monte Carlo method combined with the Optimal Computing Budget Allocation (OCBA) simulation optimization technique is employed to assess the performance of different strategies. A case study of the upper air routes in central and southern China shows that the proposed mode l can be readily implemented to simulate different kinds of air traffic flow management strategies and predict the effect of changes on the airspace system. It also shows that the proposed alternative collaborative route selection strategy is an effective way in alleviating the en-route traffic congestion.