This research aims to find out whether and how media agenda, political orientation, and media bias were associated during the 2019 Hong Kong protest. The research adopted the content analysis of the news coverage collected from three Hong Kong mainstream online news media -- Wenweipo, Apple Daily, and Mingpao. A total of 450 online news articles were quantitatively coded based on media agenda, media bias, emotion in media agenda, and political orientation. Descriptive analyses indicate that Apple Daily and Wenweipo mostly contained low diversity agendas whereas Mingpao contained moderate diversity agendas. Apple Daily’s news reports were slightly emotional, Wenweipo’s reports ranged from slightly and highly emotional whereas Mingpao’s reports were emotionless. In terms of political orientation, Apple Daily was libertarian, Mingpao was centrist while Wenweipo was authoritarian. Apple Daily and Wenweipo mostly contained contents with bias by commission and bias by story selection whereas Mingpao mostly contained unbiased contents. Due to the results of Chi-Square Analysis, the relationship between media agendas and media bias (HP#1) and the relationship between emotion in media agendas and political orientation (HP#2) were partially supported while the relationship between political orientation and media bias (HP#3) was significantly supported. In summary, the agenda-setting patterns of news media not only revealed their political orientation but also triggered different types of media bias. News media with polarized political orientation tended to be more emotional in their news reports. The findings confirm the universal existence of media bias, remind the general public of the tendency to be misled by media agenda setting; and, most importantly, increase a mutual understanding between social groups with different political orientations.