In the information age, people's stand tends to be extreme rather than moderate, one of the main reasons is selective exposure. Selective exposure means that individuals choose to be exposed to the information environment with belief-consistency, which is manifested in the fact that individuals are more willing to choose information with belief-consistency for reading, rather than information that challenges the original beliefs. In the Internet era, people choose information more freely and conveniently, which enlarges the harm of selective exposure. Therefore, the theoretical explanation of selective exposure has become the focus of attention of researchers. On this topic, there still is a theoretical dispute between the theory of evaluation bias and the theory of cognitive dissonance. In order to explore the relationship between evaluation bias and selective exposure, and to verify the possible regulatory effect of emotion on both, this study took "mobile phone radiation and health" as the theme, compiled eight related web page links and presented them in the form of real search context. First of all, 147 college students' belief-consistency was measured. After reading the web links, the subjects were asked to evaluate their credibility, positive and negative emotions, and further information selection. Through the moderated mediating effect, the data were statistically analyzed in order to obtain the overall model among belief consistency, credibility evaluation, emotion and information selection. Data analysis showed that the belief-consistency of college students indirectly affected information selection through the complete mediating effect of credibility, while positive emotion plays a moderating role in the influence path of credibility information selection, forming a moderated mediated model. The results showed that there was a completion mediation effect between belief-consistency, credibility and information selection, that is to say, evaluation bias is the direct cause of selective exposure. Individuals do not blindly choose information, and credibility evaluation of information is the premise of information selection. Therefore, evaluation bias theory rather than cognitive dissonance theory is a more direct theoretical explanation of selective exposure. Meanwhile, positive emotion moderates the relationship between credibility and information selection. Under the condition of high positive emotion intervention, individuals may still choose the information even if their evaluation of the reliability of the current web link is not strong. With the help of cognitive dual processing model, it can be explained that high positive emotion plays a more significant role in heuristic processing. In future research, it is feasible to explore the causes of evaluation bias and distinguish different mechanisms of cognitive emotion and thematic emotion.