Abstract: Knowledge Democracy provides a new way of legitimatizing knowledge production, which aims for solving the crisis of trust in knowledge. It endows knowledge production with certainty, equaltiy and pbulic trust. However, democracy has never been unconditional. Similarly, knowledge democracy is also constrained by subjectivity and publicness. Subjectivity is represented by the development in public spirit, multi-governance models and a culture of lifelong learning, and the corresponding requirement on individual rationality, responsibility and individual knwoledge; publicness varies a lot in odifferent disciplinary knowledge and different phases of knowledge producion. Knowledge domocracy, as a new trend in theory, is inevitable and in line with social practice. However, it also faces great difficulties and chanllenges. It has an impact on traditional public policy-making, social governance and democracy. It also requires combating with different interests in knowledge production and being considered and developed in a more grand scale.