Abstract: Based on modern American legislation and judicial practice, the article analyzes the major issues on the proof of foreign law in the U.S. courts. Beginning with the premise that the nature of foreign law has been changed from "fact" to "law" the article goes on to discuss the channels and the procedures of the proof of foreign law, and the remedies for the mistake of the proof. In the end, the conclusion is drawn and the comments and suggestions on the relevant sections in the Chinese textbooks of private international law are put forward.