On the content analysis of “Prism scandal”，this paper pays attention to the mainstream network medium’s agenda of national security，concludes the following conclusions：Commercial websites’ topics attention lasts longer；International relations and national security are the core issues of theme discourses；News websites play a leadership role in the reporting agenda of national security issues；Mainstream network medium coverage is priority to declarative reports，critical reports is priority to rational framework；Texts is the most important report forms，and Xinhua’s original coverage are reprinted up mostly；Objective and neutral are the basic reporting tendency，news websites play an important role in opinion guidance and supporting in against the United States. But，in contrast，the mainstream network medium’s agenda also has some spread defects，such as the passive position in agenda-setting，the insufficiency in public opinion guiding and the weakness emotions-guiding of internet-users，and the construction of responsibility consciousness and balancing fulcrum is future development trends of mainstream network medium.