It has been much concerned that social media, characterized by ideology-based selective exposure, would polarize public opinion, intensify partisan con?ict, and divide the society. Using Agent-based Modeling (ABM) to simulate opinion evolution in an artifcial society, Moore State, this study is an attempt to understand the relationship of social media with opinion polarization in the context of political communication. The results show: (1) There is no causal connection between social media and polarization; (2) Social stability, media intervention, and credibility of established mainstream media would all contribute to the outcomes of opinion evolution; (3) Only under the conditions of social instability and damaged credibility of mainstream media, social media could increase the opinion polarization markedly. The emergence of the opinion polarization, the limits of this simulation, and methodological implications of ABM approach are also discussed.