The profound reshaping of public communication by Chinese social media platforms necessitates a critical analysis of their distinct impacts on the contemporary public sphere, with particular emphasis on the student population and the educational process. This article aimed to systematically analyse and compare the operational logics of Weibo, WeChat, and Douyin, evaluating their specific influences on the formation and fragmentation of rational public discourse, especially among students. A comparative case study methodology, grounded in a theoretical framework of the public sphere, was employed to examine the three dominant platforms. The analysis traced Weibo’s transition from an open square for public agenda-setting to a space dominated by commercialisation and entertainment, which shrinks the arena for substantive debate and models communication norms for young users. WeChat’s private, strong-tie ecosystem was shown to foster information encapsulation, creating formidable circle barriers that hinder the cross-cutting flow of public information and can limit students’ exposure to diverse perspectives. Douyin’s core algorithmic distribution mechanism, while enabling unparalleled content delivery efficiency, simultaneously intensifies cognitive domestication and systematically deconstructs complex public issues into simplified entertainment. These platform dynamics carry significant pedagogical, psychological, and sociological consequences for students, including decreased attention spans, diminished capacity for critical thinking, and impacts on social cohesion through fragmented discourse. The practical value of this research lies in its potential to provide a structured framework for regulators, platform designers, and educators to develop targeted strategies – such as algorithmic transparency, multi-stakeholder governance, and enhanced digital literacy curricula – to mitigate these negative effects and foster a more robust, inclusive, and educative public communication environment