Communication scholars are beginning to pay more attention to the role of media in political polarization with studies on the effects of partisan media and selective exposure on polarization. However, the way media portray political reality may also cause mass political polarization. This dissertation attempts to explore how journalistic routine leads to political polarization. News media and journalists tend to focus on political conflicts between major parties rather than on issue content. Does this concerning news reporting behavior encourage the psychological processes of polarization? By linking framing effect theory with social identity and self-categorization theories, this study explores how news frames affect political polarization of audiences through party identification processes. The theories of social identity and self-categorization suggest that intergroup conflict makes group identity salient, and when group identity is salient, it becomes a basis for perception and judgment. Based on that, this dissertation empirically examined the process of [political conflict news frame à party identity salience à political polarization] by manipulating group cue and level of conflict in a news story about genetically modified foods in a 2 (group cue: political frame vs. scientific frame) × 2 (level of conflict: conflict frame vs. consensus frame) web-based experiment (N = 367). The results showed that political conflict news frame positively affected party identity salience, perceived polarization, and attitude polarization, but did not influence affective polarization. In addition, mediation tests suggested that party identity salience did mediate the effects of political conflict news frame on perceived polarization and attitude polarization. However, a mediating effect of party identity salience on affective polarization was not found. This study empirically showed that news frames can accentuate party identity salience when partisan audiences process the news story and that party identity salience is a key factor in explaining partisan audiences’ political polarization over an issue. Political conflict news frame plays an important role as a contextual/situational factor that momentarily increases people’s political identity salience, resulting in perceptual and attitudinal political polarization. Theoretical and practical implications as well as directions for future study are discussed.