Significance of the problem stated in the article is stipulated by the fact that professional self-determination of students at the stage of professional education needs pedagogical support; using resources of additional education program will let the individual make smart choices about future professional sphere. Object of the article is to work out and prove theoretically the subjective-developing support system of professional self-determination among teacher-training university students in the condition of additional education program implementation. Main research approaches to the problem are subjective and pragmatic approaches that let us see a personality not as a selection of objective characteristics in the space of diagnostic criteria, but as a carrier of a certain world view, as a complex of individual values and points. Structure of the represented subject-developing system of professional self-determination support for students of teacher-training university includes interdependent components, that help detect hidden potential and make it active--diagnosing, motivational, organizational, informative, and reflexive. Subject-developing system is meant to improve level of students' professional self-determination, which influences such characteristics as personal activity and responsibility, graduates' competitiveness level in the labor market in a good way.