Objectives To evaluate the effect of extra-oral mirror-inverted operation training using the mirror operating device among the second-year students of stomatology. Methods Longitudinal study was adopted in this study. A total of 40 students majoring in 2019 five-year stomatology program from the Fourth Military Medical University were included. Participants used the improved mirror operation training device to conduct extraoral mirror operation training. The number of error positions and horizontal line angles of the students between different exercise times were recorded. One-way ANOVA was used to compare the difference between the number of error sites and the angle of the horizontal line of the trainees between different exercise times, and the questionnaire was used to collect the trainee's feelings about the impact of the extra-oral mirror operation skill training on the intra-oral operation. Results The error points in five different exercises were [(9.60±3.39), (7.75±2.97), (6.28±2.44), (5.63±2.55), (3.18±2.63)], and the horizontal line angles were [(3.63±3.71), (2.11±3.11), (1.96±3.58), (1.63±3.11), (1.33±1.40)], respectively. It was found that the number of error points and horizontal angle decreased significantly with the increase of practice times. The results of the questionnaire showed that 95.0%(38/40) of the students considered that mirror-inverted operation training was very helpful for intraoral operation. Conclusions Students' extra-oral mirror operation skills could be improved in short time. And the skills could be maintained during a period of time.