Abstract: ［Purpose/Significance］Users’ attitudes and responses of social Q&A sites to public health emergencies can reveal the characteristics and evolution of their health information needs.［Design/Methodology］Taking the posts in Baidu Knows and Zhihu as research objects, this paper built a coding system of users’ health information needs on social Q&A sites in public health emergencies. First, users’ health information needs were analyzed through a multidimensional scale analysis. Then the changing rules of posts amount and users’ health information needs were revealed from the perspective of time. Finally, the differences of users’ health information needs between the two sites were discovered from the perspective of platform.［Findings/Conclusion］Social impact is the mostly concerned information need and infectivity is the unique need of social Q&A sites users in public health emergencies. The development of health emergencies can be divided into four periods, which are germination, outbreak, plateaus and recession. Changes occur both in the number of posts and the types of health information needs during the four stages. There are also differences in the distribution of health information needs and the sensitivity to time between the two social Q&A sites.
［Originality/Value］This paper conducts an in-depth analysis on the characteristics of users’ health information needs on social Q&A sites in public health emergencies, which could provide certain reference for optimizing information resource organization and information presentation mechanism.

Key words: Health information need, Public health emergency, Social Q&A site, Baidu Knows, Zhihu