[Purpose/significance] Sharing co-ownership information on social platforms has become a common and inevitable phenomenon. Understanding the co-ownership information disclosure behavior of social platform users is crucial for enhancing their co-ownership information sharing experience and protecting collective privacy. [Method/process] Adopting the grounded theory method, this study conducts a comprehensive, systematic and in-depth investi⁃gation into the characteristics, contexts and occurrence mechanism of co-ownership information disclosure among so⁃cial platform users from a collective perspective via three-level theoretical coding. On this basis, it develops a model for the occurrence mechanism of social platform users' co-ownership information disclosure behavior, which encom⁃passes 9 main categories, 19 basic categories and 102 initial concepts. [Result/conclusion] This study found that the content characteristics, subject characteristics, and audience characteristics of co-ownership information can affect in⁃dividuals' perception of collective benefits and risks. At the same time, the collective benefit and risk perception of in⁃dividuals will directly and indirectly affect their disclosure behavior of co-ownership information through collective fair⁃ness assessment. In addition, the disclosure of co-ownership information by individuals is directly influenced by their perception of information ownership and collective privacy coping. Moreover, individual perception of information owner⁃ship and collective privacy coping can also moderate the impact of collective benefit and risk perception on co-ownership information disclosure behavior. The results enrich the theoretical framework and research system of individual informa⁃tion disclosure behavior, and provide practical insights for policy makers and social platform developers to enhance us⁃ers'co-ownershipinformationsharingexperience.