dual citizen       
noun [ C ] uk/ˌdʒuː.əl ˈsɪt.ɪ.zən/ us/ˌduː.əl ˈsɪt̬.ə.zən/
 双重公民
someone who is a legal citizen (= a member) of two countries at the same time
  She became a dual citizen of Cambodia and the US. 她成为柬埔寨和美国的双重公民。 
 I am a US-Australian dual citizen. 我是美国和澳大利亚的双重公民。 
 Compare: dual national
 - More examples
 - Neither US nor Mexican law forbids dual citizens from voting in both nations.
 - He is a dual citizen of Jordan and the USA who has lived in Seattle for 20 years.
 - I have family that are dual citizens or that live in the US as Canadian citizens.
 - He was born and grew up in Edinburgh but he is a dual citizen - his father is a former US serviceman.