The purposes of this study were to outline nursing competences and to develop credentialing model of the essential community psychiatric mental health nursing. The action study research method was used in the study, with a core group of research subjects recruited from the field of psychiatric mental health nursing education and clinical practice. The construct of the developmental model comprises five stages: preparation stage, formation stage, exercise stage, communication stage, and operation stage. The developing process of discussion, clinical practice, reflection, and re-modification, produced the following results. 1. Constructing the essential competence framework of community psychiatric mental health nursing. 2. Constructing the essential competence credentialing model of the community psychiatric mental health nursing. These results might serve as a basis and a reference for sustained community psychiatric mental health nursing.