Aesthetic education (Meiyu) is globally recognized for its unique capacity to cultivate human moral character. However, within the field of music teacher education, existing research on Pedagogical Content Knowledge (PCK) has predominantly focused on the accumulation of instructional strategies and technical skills, often overlooking the internal ethical drivers that sustain professional excellence. This study addresses this gap by investigating the complex factors influencing the PCK development of exemplary music teachers in China. It proposes that an intrinsic, virtue-based drive—termed Moral Awareness (Dexing Zijue)-functions as the central engine of their professional growth. The primary aim is to construct a substantive theoretical model that explicates the mechanism through which Moral Awareness transforms a teacher's professional identity and pedagogical practice. To rigorously address the research questions, this study employed a hybrid methodological design that strategically integrates Multiple-Case Study (Yin, 2018) with Constructivist Grounded Theory (Charmaz, 2014) . This dual approach was selected to resolve the tension between contextual particularity and theoretical generality, a common challenge in educational research: We utilized a multiple-case design to establish the ecological boundaries of the research. This ensured that the unique cultural, institutional, and regional contexts of each teacher were preserved, preventing the data from becoming decontextualized abstractions. Within these bounded cases, Grounded Theory served as the analytical engine. Rigorous coding procedures (initial, focused, and theoretical coding) and constant comparative methods were applied to transcend individual case descriptions. This allowed for the extraction of a unified, abstract theoretical model regarding the "Moral Awareness" mechanism that holds true across different cases. To ensure the study's conclusions are robust and representative of the diverse Chinese educational landscape, a multi-stage purposeful sampling strategy was executed, combining criterion sampling and maximum variation sampling : Participants were strictly selected based on peer recognition and sustained excellence in aesthetic instruction to ensure information-rich cases. Crucially, to mitigate regional bias, we recruited 15 teachers representing China’s seven major geographical regions (North, Northeast, East, Central, South, Southwest, and Northwest China) . This extensive geographical coverage ensures that the identified mechanism of Moral Awareness is not an artifact of a specific local subculture (e.g., the wealthy coastal East) but a fundamental professional trait shared by expert teachers across mainland China. Data analysis revealed five major categories impacting PCK development: Individual Beliefs, Continuous Practice, Critical Incidents, Significant Others, and Environmental Factors. However, the study's most significant contribution is the identification of Moral Awareness as the core category that unifies these factors. The resulting theoretical model demonstrates that Moral Awareness acts as the internal genetic code, driving teachers to voluntarily engage in deliberate practice and reflection despite external constraints. It mediates the transformation from a biological "Natural Self" to a professional "Moral Self," providing the spiritual stamina required for high-quality aesthetic education. This study challenges the prevailing competency-based models in teacher education by highlighting the primacy of the "moral dimension." It suggests that fostering high-quality aesthetic education requires shifting focus from external performance indicators to the cultivation of teachers' inner moral structure. Furthermore, by anchoring the findings in data from seven distinct geographical regions, this research offers a validated, localized theoretical framework that contributes a significant "Chinese Voice" to the global discourse on teacher agency and PCK.