Abstract: In twentieth century, Karl Popper was one of the most influential thinkers not only in philosophy of science, but also in political theory. He systemically discussed the theory of democracy and made many new arguments from the view of critical rationalism. Popper converted the fundamental problem of politics from “who should rule?” to “how can we so organize political institutions that bad or incompetent rulers can be prevented from doing too much damage?”, revealed the paradox of traditional democracy theory, insisted that the essential difference between democracy and tyranny was that democracy makes it possible to get rid of a government without bloodshed, argued that democracy is valuable because it can protect individuals' freedom, and believed that the two-party system is better than proportional representation and seems to be the best form of democracy. This article reviewed Popper's theory of democracy and made some comments.

Key words: Karl Popper, Democracy, Freedom, Open society, Two-party system