Abstract: The United States' cyberspace policy is mainly reflected in the documents from the government and the military. It has been almost 20 years since Executive Order 12864 of 1993 related to the development of the National Information Infrastructure was promulgated. Most government documents on cyberspace were issued by the White House, which barely touched upon international law. Their military counterparts range from documents from Department of Defense, the Army, the Navy and the Air Force to judge advocates' references. Although these military documents did mention about international law, in-depth analysis were scarce. The United States' cyberspace policy has experienced a long-term evolving process during which four tactics were employed and four characteristics were formed. International Strategy for Cyberspace, issued by the White House in May 2012, finally made it clear that the United States would adopt a radical cyberspace policy via connecting certain acts in cyberspace with using force in the real world. It will pose grave challenges to international law and international legal order for not only would the traditional concepts of territory and sovereignty be overthrew and the meaning of using force be expanded, but also the right to self-defense would be further abused and the international society be more reluctant to accept the definition of aggression. Moreover, the neutral institution in international law would be nullified, the responsibility settings in international law would be challenged, and the foundation of law of war would be destroyed.