The research in this paper introduced a single-valued metric for post-operatively rating the performance of achieved traffic flow against targeted traffic flow into an airport or sector of space.In analysis,concerned major aspects factors especially including the cost of flights movements, the solution about how to compute traffic flow rate control index was given by integrating concrete sample.At same time,the meaning of this metric was interpreted and how to apply traffic flow rate control index on evaluation ground delay program performance was pointed out.