<p>The Rural Comprehensive Practical Activity Course (RCPAC) plays a vital role in advancing quality education, fulfilling the fundamental goal of moral development, and promoting the modernization of rural education. Despite its significance, RCPAC currently faces the pressing challenge of maintaining high-quality implementation over time. Addressing the root causes of this unsustainability is essential for refining course design, improving implementation strategies, and ultimately enhancing the overall quality of the course. This study employs a qualitative research methodology, involving in-depth interviews with 42 RCPAC teachers. Guided by the core principles of grounded theory and supported by the qualitative analysis software NVivo11, the study conducts a three-stage coding to systematically identify and summarize the factors contributing to the lack of sustainable high-quality implementation. The analysis reveals that the sustainability challenges stem from the combined impact of six interrelated factors: teacher cognition, course resources, evaluation systems, school interventions, top-level design, and the teaching staff. These factors do not operate in isolation or correspond mechanically to the issue of sustainability. Instead, they interact dynamically, forming a complex network of mutual influence. These findings offer valuable insights for optimizing the design and implementation of RCPAC. Furthermore, they provide a practical reference for rural educational institutions seeking to develop more effective educational policies and teacher training programs.</p>