Every communication medium – from pamphlets, newspapers, radio to television – has two-sided influences in politics. On the one side, they can buttress authoritarian governments. On the other side, their potential in democracy promotion is also magnificent and undeniable. Especially in digital age, the improvement in freedom of expression has been more and more associated with the impact of the Internet, new media and mobile phone communication. For China, while its economic development and military power are rapidly enhancing, the possibilities of improvement in participatory politics and democracy turn into a big question. With the quick rise in information and communication technologies (ICTs), the realization of ―cyber democracy‖ and the growth of public sphere have become a wishful thinking for the Chinese people. This thesis, by choosing the role of public sphere as a main theme, will mainly discuss the changing interactions between the government of People's Republic of China (mainland China) and citizens' freedom of expression. On the basis of comparison with the Western and other two East Asian countries (Japan and South Korea), the purpose of this thesis is to see how mainland China's public sphere has been transformed together with the changes in politics, economy and technology; and to find the uniqueness of China's public sphere and Internet-based political activism.