This article is based on the theoretical framework of cognitive dissonance theory. The purpose is to test whether two opposing social facts determine people ’s dissonance towards the motherland and how they use selective media exposure to solve this disparity. The two opposing facts are nationalism--positive belief about the country ’s prosperity，and perceived media credibility--explicit negative characteristic of autocratic country. The dissonance is the valence difference between above two concepts. Selective media exposure is people ’s intentional media use on local/foreign media under positive/negative situation of China. The method is cross regional comparison by survey data in Shenzhen（Mainland China）and Hong Kong. The comparison puts the theory in different social and cultural context. Statistic data partly supports the hypotheses. There are regional difference on nationalism，media credibility and dissonance. But correlation between dissonance and selective media exposure is not verified. Discussion is led from the angle of media ecology.