I an in transit from Beijing to U.S.A. overnight can I exit out the airport without a visa

Hi, it is ok. US passport are allowed free transit via Beijing airport if the stopover is less than 72 hours. So, it is ok for you to get a free transit permit after arrival at the airport (a stopover less 24 hours); or apply in advance through your airline before landing (if the stopover is longer than 24 hours but less than 72 hours).