Social media has become one of the primary channel for the public to obtain emergency science popularization information. In the social media context，emergency science popularization on mainstream media may reduce the cost of obtaining and identifying emergency science information for the public and promote the public to make sense of the risk and respond effectively. This study uses manual and computer-driven content analysis methods to examine the content of science popularization messages in People’s Daily microblog during the Covid-19 epidemic. The results show that emergency science popularization on People’s Daily microblog was situation-oriented to satisfy the public information needs and relied on authoritative sources to ensure the contents accuracy and reliability. It interpreted risks objectively and corrected misinformation continually to promote public understanding of the disease. In addition，sufficient efficacy information was transmitted to provide reliable guidance for the public. The study also indicates that knowledge about treatment and authoritative sources were significantly associated with greater public engagement. Accordingly，this study further illustrates the importance and mechanisms of situational factors and authoritative experts in mainstream media’s emergency science popularization，and explores the possibility of public participation in the collaborative network of emergency science popularization in social media context.