[Purpose/Significance] Academic communication has now expanded into multi-scenario online interaction. Content-based social platforms such as Zhihu and Rednote, with their massive user bases and abundant topics, are becoming new venues for academic exchange. Investigating the thematic characteristics of academic communication on content-based social platforms can help optimize the platforms' academic communication functions, enhance users' academic information literacy, and encourage more users to engage in high-quality academic exchange, thereby accelerating research innovation and knowledge dissemination. [Method/Process] First, a research framework for academic communication behavior on content-based social platforms was constructed based on the S-O-R theory. Second, Python web-crawling techniques were employed to collect interactive comment texts under Zhihu's academic topics and Rednote's academic tags from January 2020 to October 2025. After preprocessing including screening, deduplication, and synonym merging, jieba word segmentation and stop-word filtering were applied for text processing, and sentiment classification was conducted based on the Dalian University of Technology sentiment lexicon. Finally, the BERTopic topic model was adopted to mine thematic characteristics, and an in-depth analysis of academic communication behavior on content-based social platforms was carried out. [Result/Conclusion] A large number of users have already chosen to conduct academic communication and interaction in the comment sections of social platforms. The user behavior characteristic topic model constructed on the basis of the S-O-R theory can effectively reveal users' core needs in informal academic communication. The findings show that academic topics are mainly concentrated in such aspects as literature reading and research practice, academic psychology and emotional resonance, academic social networking and career development, and disciplinary fields and institutional exchange. These conclusions provide empirical evidence for social platforms to optimize academic communication functions, improve the quality of communication, and guide a healthy academic ecosystem.