[目的/意义]Z世代用户群体已占据我国社交媒体用户逾半数比例，该群体具备“‘热梗’即语言”、以技术 机制对抗社交媒体不利影响、使用需求分层与“类Finsta”文化的特点。了解Z世代用户在社交媒体中的信息发布 行为特点，能够为理解其使用偏好提供实证参考。[方法/过程]通过理论抽样，对12名在同一社交媒体平台中同 时拥有主副账号的Z世代用户开展半结构化访谈，并以扎根理论方式分析访谈转录稿。最终形成Z世代用户对社 交媒体的使用目的、隐私认知、人际关系认知、信息接收者认知、社交平台的空间划分和社交媒体信息发布行为这 6个理论范畴，并讨论了18个具体范畴间的关系，以及3条用户从主、副账号间的迁移路径。[结果/结论]Z世代用 户“去社交化”“情绪表达与自我调节”和“自我发展”的社交媒体使用需求，促进其对社交平台空间的再划分。该 信息实践创造并强化了“副号即隐私”的认知，使Z世代用户通过控制信息发布的时空范围、内容语境和发布频次 的方式，实现隐私边界的动态平衡。文章同时基于该特征从平台和用户角度讨论了用户体验优化的具体措施。

[Purpose/significance] Generation Z (Gen Z) users account for more than half of China’s social media us⁃ ers. Their social media culture characteristics including (1) meme as a language，(2)leveraging the technology to cope with the negative influences that social media platforms posed，(3)Finsta culture. Understanding Gen Z users’informa⁃ tion posting behaviors in social media, can provide empirical references for understanding their preferences on their us⁃ age and intentions of Internet activities. [Method/process] Through theoretical sampling, semi-structured interviews were conducted among 12 Gen Z users who had both primary and secondary accounts on the same social media plat⁃ form. Based on grounded theory, the transcript of the interviews was analyzed. Finally, 6 core categories are identified, namely, Gen Zs’use purpose on social media, privacy cognition, interpersonal relationships cognition, information re⁃ ceiver cognition, spaces’boundaries setting on social media, and social media information posting behaviors. The rela⁃ tionships among the 18 specific categories and the 3 transformation paths of users’migration were discussed. [Result/ conclusion] Gen Z users“social disconnections”“emotionexpressionandself- emotion regulation”,and“self- develop⁃ ment”usage needs on social media promote their resetting on spaces within same social media platform. Such informa⁃ tion practice creates and enhances Gen Z users’new cognition on online interpersonal interaction that is“Secondary Account as Privacy”. Based on such cognition, Gen Z users can redefine the boundaries of“privacy space”on social media, by controlling the posted information’s scope, content’s context, and frequencies. Based on that, this paper dis⁃ cusses the user experience optimization service approaches, from the perspective of the platform and users.