Abstract: Grassroots social governance represents a crucial domain for the indigenization of social work, in which mediation serves as a key area of practice. In the context of rural social transformation, conflicts and disputes have become increasingly complex and diversified, placing higher demands on the professional competence of rural mediators. Grounded in capacity building theory and social ecosystem theory, this study adopts a case study approach, focusing on the capacity building of mediators in H Village, a mountainous area in Yunnan Province. Through participatory observation, in-depth interviews, and quantitative assessment, the study explores the enhancement of mediators’ competencies through group work intervention and proposes pathways for optimizing the mediation ecosystem. The findings reveal that: on the one hand, group work, through interactive learning and continuous follow-up, can effectively improve mediators’ cognitive abilities, knowledge base, and professional skills; on the other hand, the synergistic optimization of the social ecosystem can provide long-term support for the capacity building of rural mediators. This paper contributes to the empirical research on rural mediator capacity building by integrating capacity building theory and social ecosystem theory, offering both theoretical insights and practical models for grassroots mediator development, which holds practical significance for improving mechanisms for conflict resolution in rural areas.