Abstract: [Purpose/Significance] This paper aims to construct a three-level analytical framework from the perspective of mechanics, to not only parse the basic elements of individual dynamics but also reveal the multiple relationships between dynamics, thereby systematically present the complex characteristics of the knowledge co-creation group dynamics in online health communities. [Design/Methodology] In this paper, 17,168 valid comments from 414 discussion posts obtained from a platform of "Dances with Cancer" were used as the data source. Firstly, at the micro-level, we clarified the specific types of group dynamics and their basic elements（size, direction and point of action）through three levels encoding. Then, at the meso-level, after standardizing the comment texts, the coupling coordination degree was calculated to reveal the coupling relationships between pairwise dynamics. Finally, at the macro-level, a system dynamics model with the three-dimensional dynamic was built from the macroscopic perspective, and the chaotic relationship between the three-dimensional dynamic was examined through the scenario simulation analysis. [Findings/Conclusion] The group dynamics of knowledge co-creation in online health communities encompass information support, emotional support, and patient compliance. Information support exerts its basic driving force through the two action points of group consistency and group cognition level; emotional support exerts its centripetal derived force through the two action points of relational perception and emotional perception; while patient compliance exerts positive binding force through the action point of health belief. The relationship between the two dynamics presents different coupling stages and coordinate features. The effect of 10% increase in three-dimensional dynamics on knowledge co-creation is greater than that of 30% increase in single dynamics, indicating a clear synergistic effect resulting from the chaotic relationship between group dynamics.[Originality/Value] This paper analyzes the group dynamics of knowledge co-creation from the perspective of mechanics, and reveals the individuality ,relevance and wholeness of group dynamics, as well as provides new ideas and references for the study of group dynamics in online communities.

Keywords: Online health communities, Knowledge co-creation, Group dynamics, Coupling analysis, System dynamics