The purpose of this research mainly lies in exploration of influence of psychological capital of preschool teachers on professional commitment, and moderation effect of their working years on the influential relationship between psychological capital and professional commitment. 400 Taiwan preschool teachers took part in this research as the subject to receive measurement of Psychological Capital Questionnaire along with Professional Commitment Scale, and the extracted data underwent analysis of structural equation modeling with use of LISREL software. From the analysis results, it is found that psychological capital of preschool teachers has significantly positive influence on professional commitment, which means that as preschool teachers possess more psychological capital; their professional commitment will get higher correspondingly. In addition, for preschool teachers' working years demonstrates significant moderation effect in the causal correlation of psychological capital to professional commitment, signifying that as working years of preschool teachers increases, influence of their psychological capital on the professional commitment will become better. Finally, based on research findings, we proposed suggestions to preschool teachers, kindergartens, and governmental institutes in how to enhance psychological capital and professional commitment of preschool teachers.