On March 11, 2011, Japan was struck by a massive earthquake and tsunami. The tsunami caused tremendous damage and traumatized children. We aimed to evaluate and compare the changes in the traumatic symptoms of high school girls 8, 20, 30, and 42 months after the 2011 tsunami. The Post-Traumatic Stress Symptoms for Children 15 items (PTSSC-15), a self-rating questionnaire on traumatic symptoms, was administered to 811 high school girls at the above-mentioned intervals. We calculated the total score, post-traumatic stress disorder (PTSD) subscale, and depression subscale of PTSSC-15. The total score was correlated with house damage, evacuation experience, and bereavement experience. The PTSSC-15 total scores of high school girls with traumatic experience were significantly higher than the scores of children without these experiences (all p < 0.0001). The PTSSC-15 total score did not decrease significantly over time. Furthermore, the PTSD subscale of the PTSSC-15 did not significantly improved over the study duration. However, the depression subscale of the PTSSC-15 significantly improved at 30 months, but significantly worsened at 42 months (both p < 0.0001). This study demonstrates that the traumatic symptoms of high school girls who survived the massive tsunami fluctuated unpredictably with time. Nonetheless, high school girls continued to suffer depressive symptoms (insomnia, withdrawal, appetite loss, inattention, and physical symptoms) after 42 months.