Teachers' self-efficacy and engagement in classroom teaching play critical roles in making the integrated science, technology, engineering, and mathematics (STEM) education happen. However, the potential factors influencing teachers' self-efficacy and engagement in STEM teaching have yet to be examined. This study constructed a hypothesized model including teaching self-efficacy, pedagogical design self-efficacy, discipline knowledge, administration support, and collegial support and investigated their structural effects on teacher engagement based on the survey of 458 Chinese teachers. Results of structural equation modeling revealed teaching self-efficacy, pedagogical design self-efficacy, and collegial support were the important predictors of teachers' engagement in STEM teaching. Meanwhile, teachers' discipline knowledge and administration support positively influenced teaching self-efficacy which in turn influenced teacher engagement. Findings of this study suggested that to enhance teachers' engagement in STEM teaching, further studies on teacher professional development are needed to explore how to enhance teachers' pedagogical design competencies and collaboration consciousness. This study provides some implications and recommendations for school administrators and teacher educators to successfully enhance teachers' engagement and competencies in STEM education.