The purpose of this study was to explore factors related to the professional development of art therapists, such as art arbitration awareness, self-reflection, and supervision, and to demonstrate the relation of influence between variables. The participants in the study were 281 domestic art therapists, and the collected data were analyzed statistically. The results of this study were summarized as follows. First, it was found that the recognition of art intervention, self-reflection, and supervision directly affected the professional development, self-reflection, and supervision. Second, as the result of analyzing the mediating effect of the major variables, it was found that the recognition of art materials indirectly and significantly influenced on the professional development of art therapists by self-reflection and supervision. Third, the mediating effect of self-reflection was significantly higher than that of supervision, and the results of art intervention recognition and professional development were insignificant in the process of confirming the parameters between the two factors. This is an important result that doing art work without recognizing self-reflection does not affect professional development.