CNOOC' s acquisition on UNOCAL was the largest acquisition of China in the recent years . However，CNOOC had to give up the deal because the US Congress required the strict national security review on the acquisition . The research on the case is not only beneficial for understanding the rules and procedures of national security review of USA，but also beneficial for us considering the counter-measures to secure our interest in outward FDI . Under the background of international financial crisis，the US government has adopted a series of measures to develop its economy，including loosing restrictions on the admission of foreign investment to some extent，which provides extraordinary opportunities and challenges for Chinese investors to “Go-Global”. So currently，the research on such issue is of great value.