After the judgment of the New York Times Co. v. Sullivan in 1964, American defamation law has changed from traditional nature of the common law to constitutionalization of the defamation law. The principle of “public figure” established in the case greatly broaden the space for speech. The definition and scope of the public figure by the court have undergone a complicated evolution, and they have also been relatively well recognized. In this regard, scholars from domestic and abroad have made a relatively sufficient introduction and discussion, but few of them discuss the application of “actual malice” rule. The paper takes Masson v. New Yorker Magazine, Inc. as an example to focus on the application of “actual malice” rule and its’ connotation in the common law, and analyze the objective proof of the rule and changes to the procedural law in libel action.