Hot Weibo is an official app offered by Sina to highlight the popular Weibo posts. It measures the hotness of posts by the number of views, forwards, comments, and compliments. The top 100 hot Weibo posts are listed by Sina every day, which concentrate on that day's most important issues and become a microcosm of online public agenda in China. Through the prism of Hot Weibo, this study asks three questions: (1) what are the dominating agenda on Weibo, (2) who set these agenda and in what ways, and (3) how are these agenda distributed on Weibo?  Results show that social and entertainment issues dominate online agenda on Hot Weibo, which indicates a convergence of public space and private space in the Chinese microblogosphere. The distribution of discursive power on Weibo mirrors the power relationship in the real society. While elite users constitute the majority of hot Weibo contributors, grassroots users do have a chance to participate in the public sphere. In some cases, those nobodies who do not have many followers can also become agenda setters on Hot Weibo because of the high value of their Weibo posts. Content is the most important factor that determines the degree of hotness of a Weibo message, whereas the form and narrative do matter in boosting Weibo appeal. This research found that more than 70% of the Hot Weibo samples have pictures, which suggests the importance of visual element in blogging. Meanwhile, as news and information can help a post become a Hot Weibo, comments and opinions can also become top Weibo posts, which is sometimes more powerful in influencing public opinion. The agenda on hot Weibo are normally trivial and divergent. Once a breaking public event happens, however, people tend to speak in one voice and a strong collective consciousness will emerge. Weibo agenda will instantly amalgamate and lead to remarkable social cohesion. However, there are still a few limitations in the study. First, the categorization of Weibo contributors and Weibo themes could further be refined. The current categorization is based on the observation of the overall samples, and the scope and levels of the classification might not be optimum. In particular, the ''other'' category in theme has a similar high average degree of hotness to the ''social issues'' category, but does not have a more accurate description. Second, the sample size is limited. Only the first five Weibo posts on the chosen days were analyzed. To increase the representativeness, future studies could utilize data mining techniques to conduct more representative surveys of Hot Weibo.  Oftentimes, we hear a hubbub of voices on Weibo, but underneath such hubbub, we can always see a tendency towards consensus. There is always something that can temporarily stop people's trivial interests and private discussions, and direct people's attention to a public issue. The value of Weibo is exactly the power to build a relatively free market place of ideas in which public members determine what are the most important issues facing the society by choosing what to and what not to talk about on Weibo. Nevertheless, whether Weibo is too chaotic or too focused to serve as a better institution than traditional mass media in fostering democracy is a question we need to further consider.