Factors Influencing Vocational Education and Training Teachers’ Professional Competence Based on a Large-Scale Diagnostic Method: A Decade of Data from China

China has the world’s most extensive vocational education and training (VET) system, and VET teachers are central to training high-quality technical and skilled workers. This study aimed to explore the factors influencing VET teachers’ professional competence based on empirical research. We used a large-scale diagnostic method based on the competence measurement of VET, the teachers’ professional competence model. Comprehensive diagnostic tasks, assessment criteria, and test protocols jointly developed by Chinese and German researchers were used to diagnose professional competence. Background questionnaires were collected from 601 VET teachers in 39 vocational colleges and schools in China over ten years. Path analysis was used to explore factors influencing the professional competence of VET teachers. The study found that skill awards, highest academic degree, course type (practical over theoretical), highest level of professional qualification, and enterprise support positively influenced professional competence. School support negatively influenced VET teachers’ professional competence. Organizational identification mediated the relationship between enterprise support, school support, and professional competence. However, professional identity or learning strategy aren’t mediated the relationship between enterprise support, school support, and professional competence. This study provides an empirical basis for enhancing VET teachers’ professional competence and facilitating further development of theories regarding the professional competence of VET teachers.