paper tiger
noun [ C ] disapproving uk/ˌpeɪ.pə ˈtaɪ.ɡər/ us/ˌpeɪ.pɚ ˈtaɪ.ɡɚ/
纸老虎（指外强中干的敌人或国家）
something, such as an enemy or foreign country, that seems very strong and dangerous but is really weak and not harmful
The Soviet Union was suddenly revealed as a paper tiger. 苏联突然被揭出了纸老虎的原形。