city of xxx是xxx市的意思，所以
the capital city of Beijing，實際應該斷為the capital， city of Beijing
意為：首都，北京市
另外我查了壹下wikipedia，妳說的那句話大概是這句吧：
The PRC is a single-party state governed by the Communist Party, with its seat of government in the capital city of Beijing
翻譯如下：中華人民***和國是由***產黨壹黨執政的，其政府位於首都北京市