Driving route: From T3, take the direction of Jingping Expressway (1, Terminal 2), then take the direction of Airport Expressway (Beijing downtown) for 2 to 3 kilometers, drive to Wuyuan Bridge (with road signs, Fifth Ring Road, Jingcheng Expressway and Beijing-Tibet Expressway), take the Fifth Ring Road to Xiaojiahe Bridge exit (Beiqing Road, Yuanmingyuan West Road), and take the Fifth Ring Road to Yuanmingyuan West Road.
Bus route: Take Airport Bus Line 4 and get off at Beitaipingzhuang, walk to Beitaipingqiao West Station (about 40-50 meters), and take Bus No.718 to National Defense University.
I don't know if I can help you if I write clearly.