Based on the Teaching Through Interaction (TTI; Hamre et al., 2013) framework and the observational tool Classroom Assessment Scoring System (CLASS; Pianta, La Paro, et al., 2008), some professional development (PD) programs combined with video-based coaching had been developed. Previous studies have well-documented the effects of these PD programs on in-service teachers’ mastery of interactional skills; however, little research has been done on the effects for preservice teachers. In the current study, we aimed to explore: (1) if video-based coaching improves preservice teachers’ interactional skills, and (2) how the personal characteristics of teachers (whether they attend coaching or not) predict the change of interactional skills during their practicum. Using an experimental approach, the study recruited 56 preservice teachers from a Chinese university to participate in the assessment and intervention. Results showed that preservice teachers in the coaching group who received one semester of sustained and individualized coaching support demonstrated a greater improvement in teacher-child interaction skills in the Emotional Support domain than those in the control group. Further, preservice teachers’ higher levels of child-centered beliefs and initially lower levels of knowledge of effective teaching, ability of identifying effective teaching behavior, and teacher-child interactional skills related to a greater increase in interactional skills during the internship. These findings shed light on how to design effective preparation programs for preservice teachers during their practicum.