Abstract: After a critical reflection on radicalism for 20 years, more positive discussion is in need about the Chinese radicalism in the 20th century. Radicalism, which forms a triangle with the conservatism and liberalism and serves as an instrument in analyzing the modern public intellectual history, not only shows an “attitude” or “tendency”, but also embraces some substantial theoretical “doctrine”. The social foundation for its birth can only be understood from the perspective of the social history of the “revolutionary era”. The revolution in China in the 20th century is not only political and cultural, but involves a fundamental transformation in social structure as well. The period from 1895 to 1995 has witnessed the whole “rising-declining” picture of the radicalism in the “revolutionary era”. Radicalism has political, cultural, philosophical and other dimensions. Philosophical radicalism not only provides the philosophical defense but also serves as the spiritual core for political and cultural dimensions of radicalism. The philosophical radicalism includes roughly four aspects: progressivism, the doctrine of social revolution, equalitarianism and utilitarianism. A deeper genealogical analysis is required to examine how these aspects jointly lay a philosophical foundation for radicalism.