Abstract: The Supreme Court's decisions confirmed that the Fourth Amendment of Constitution applied to the electronic surveillance engaged by the government. However, it didn't applied to the information voluntarily conveyed to the third party. The Congress enacted ECPA and FISA to regulate the government surveillance for the law enforcement purpose and national security purpose. After the event of 911,the Congress enacted PATRIOT Act,which expanded the government's power to collect information. The balance between the national security and personal privacy protection has been readjusted and many disputes arose since then.