Basing on a survey in Changsha, by using SEM, This paper analyzed how different types of political discussion played mediated role between public information exposure from different channels and institutional and un-institutional political participation. The study found that： Interpersonal political discussion had played suppressing role between information exposure from traditional media and institutional political participation; Internet political discussion had played mediated role between information exposure from traditional media, website and institutional political participation; Public information exposure from government’s we media had promoted internet discussion and institutional participation, but had not positively impacted institutional political participation. With the growth of political participation, the results can a reference for government to build related institution.