Populism is a buzzword in recent western politics, throughout history, populism has exerted many influences on the course of democracy, it thrived and prospered through all the endeavors at expanding the concept of citizenship. Equality and freedom are the most fundamental meanings for democracy, with the development of democracy, the expansion in the implications of freedom and equality manifests a subtle and delicate correlation with populism. This article mainly using US as an example. US was founded on core values like freedom and equality, whereas recent years have seen a stronger presence of populism, crisis of divergence and divide is looming in politics and society. This article is written against the backdrop of USA and analyze the conventions, reforms and challenges standing in the course of American democratic history, and then provide a new perspective of analyzing populism through the lens of democratic institutions or the features of democratic society per se.