Boston Marathon bombings on April 15，2013 were another serious terrorist attacks in the United States mainland since 9.11 attacks. The Boston attacks completely shattered the myth of the U.S. homeland security after 9.11，made significant psychological impact on the U.S. common people，and caused great social panic consequences. Meanwhile，Boston bombings reflected some new trends of violent terrorist activities of the United States，such as the threat of domestic terrorism and the so-called“lone wolf”type of terrorist attack as the major threat to the United States. These trends of terrorist attack pose more new challenges for the U.S. counter-terrorism strategy.