Abstract: The Pentagon Papers (officially titled Report of the Office of the Secretary of Defense Vietnam Task Force)and the following Pentagon Papers Case relating to the Vietnam War (1955—1975)are the issues that fundamentally influenced the American politics in the 1970s.Referring to first-hand materials of official documents and personal memoirs,the public knew about the changing attitudes that former American Secretary of Defense Robert S.McNamara took from optimistic foreseeing to the disillusionment,and eventually back to reposition,which pushed him to deicide to summarize historical documents about the U.S.'s involvement in Vietnam so as to reevaluate the military actions in the Vietnam War.This finally led to the collection of the Pentagon Papers.Former United States military analyst Daniel Ellsberg also experienced a process from support to disillusionment to eventual rethinking.In order to stop the U.S.administration from further action in Vietnam,he released the Pentagon documents to the press,causing the Pentagon Papers Case.The final trial of the case made the papers available to the public,and thus they became the proof and confession of the injustice of the Vietnam War.The Pentagon Papers exposed the inside information of American policy-making on the Vietnam War,and also revealed that American War in Vietnam was immoral and dirty,which provides indispensable sources for the research on the Cold War and the international relationship history.In addition,the Pentagon Papers Case have its legal significance,invoked by lots of cases in the U.S.

Key words: the Pentagon Papers, the Pentagon Papers Case, the Vietnam War, Robert S.McNamara, Daniel Ellsberg