There is a strong ongoing debate about the impact of trust and political knowledge on institutionalized political participation. Based on social exchange theory, this study examines the roles of social trust, political trust, and political knowledge on citizen voting in grassroots elections by using logistic regression. The logistic regression analysis of this study shows that social trust, political trust, and political knowledge have significantly positive effects on the likelihood of voting in grassroots elections in China. More importantly, it finds that the level of citizens' political knowledge can positively moderate the relationship between political trust and the likelihood of citizen voting in grassroots elections. "Political knowledge" can be regarded as a kind of political self-education for citizens. In view of this, trust and political knowledge can be seen as vital preconditions for citizen voting in grassroots elections. This study suggests that the government should pay more attention to the positive roles of trust and political knowledge in promoting political participation and democracy construction at the grassroots level.