Abstract: Purpose/Significance The characteristics and patterns of the communication of public emergencies on mainstream media’s microblogs have important realistic significance to the public opinion guiding and crisis governance. Design/Methodology Focusing on the information dissemination of ‘8.12’ Tianjin Port fire and explosion on the microblog of People’s Daily, the communication mechanism of public emergencies on mainstream media’s microblogs has been revealed through data analysis in four dimensions, namely content of microblog, characteristics of users’ behaviors, social network attribute and emotions conveyed of message forwarding. Findings/Conclusions It is suggested that mainstream media’s official microblog should adopt different agenda settings at different stages of information dissemination, given the following communication mechanisms of public emergencies: users’ behaviors dominate the information dissemination on microblog, which is restricted by users’ characteristics. This paper identifies four paths of information dissemination for public emergencies. The rule of “content is king” has been replaced by “relationship wins” in “small-world networks” such as microblog. In terms of emotions conveyed, KOLs’ influence is declining, while the grassroots are awaken to participate in politics. Lastly, this paper puts forward some suggestions to facilitate the public opinion guiding and crisis governance of public emergencies spreading on mainstream media’s microblogs.