Abstract:As an important subject of science communication, traditional mainstream media plays an important role in reporting scientific events and popularizing scientific knowledge. To better understand the characteristics and effects of online science communication by traditional mainstream media on social media, this paper explores the textual characteristics of science blog posts by mainstream media and their effects on communication effects. First, we obtained more than 11,000 blog posts published by nine official mainstream media on Weibo platforms in 2021, and then filtered the scientific blogs by the selected keywords related to science communication. Through processing the text data set by LDA-based topic modeling, we summarized 29 primary topics and 7 secondary topics to obtain the overall topic distribution of science communication in mainstream media. From the view of the meaning of the detailed topics, the mainstream media both provide timely and continuous coverage of scientific discoveries and innovations, and produce and distribute popularized content including social and healthy issues that is closely related to the general public. Secondly, this paper conduced a manual coding-based content analysis on the sampled sample data set to obtain the sentiment stance and citation source of each blog post in the sample. Finally, this paper investigated the relationship between the three text characteristics featuring topic, sentiment stance and citation source and the three communication effect characterization indicators of blog posts: forwards, likes and comments. The results showed that the topic and sentiment stance had significant effects on all three communication indicators of blog posts, and the citation source showed no significant effects on three indicators. The communication effect of blog posts with the topic of popularizing scientific knowledge of social and livelihood issues and holding a positive sentiment stance was significantly better than that of blog posts of other categories. The public has different degrees of motivation to disseminate scientific blog posts with different textual characteristics, and topics closely relevant to the daily life and knowledge popularization, and more emotional resonance can trigger better communication effects.