再请教：官网看到的，不明白出境怎么用美国护照呢？

regardless of whether they hold another nationality:

• You must enter and leave the United States on your U.S. passport. You are not allowed to enter on your foreign passport, because U.S. law requires all U.S. citizens to enter and depart the U.S. on a valid U.S. passport. U.S. citizens are not eligible for a U.S. visa.