Since the increasing performance of the PLA air force and the limitation of military purchase, the combats of ROC air force are still the previous generation. This paper applied system dynamics to analyze the military capacity of ROC current combats and of PLA current combats in the air zone of Taiwan. We also compare the military capacity after upgrading in five years and ten years through scenario analysis. In final, we propose that without the possibility of new combat purchase, the suggestions of preservation of M-2000 and upgrading IDF and F-16.