To explore the dynamic relationship between depressive symptom and non-suicidal self-injury(NSSI) behavior among rural left-behind junior high school students, as well as the mediating role of social support, so as to provide a reference for preventing the occurrence of behaviors that endanger the physical and mental health of rural adolescents.

In October 2023, 828 rural left-behind junior high school students from four counties and cities in Xiangxi Autonomous Prefecture, namely Luxi County, Huayuan County, Baojing County and Longshan County, were selected by cluster random sampling for a one-year follow-up investigation (T1:October 2023, T2:April 2024, T3:October 2024). Depressive symptom, NSSI behavior and social support of junior high school students were evaluated by using the Patient Health Questionnaire-9(PHQ-9), Adolescent Non-suicidal Self-injury Assessment Questionnaire (ANSAQ), and Social Support Scale for University Students(SSSUS). A cross-lag panel model was constructed to analyze the dynamic relationship between depression symptom and NSSI behavior, as well as the longitudinal mediating role of social support.

The levels of depressive symptoms(T1-T3:150.00±5.88, 14.29±7.52, 13.97±6.70) and NSSI behavior (T1-T3:6.91±4.65, 6.10±3.92, 4.79±3.51) of rural left-behind junior high school students both showed downward trends (F=13.41, η²=0.02; F=50.49, η²=0.06), the level of social support (59.17±14.68, 62.27±15.36, 61.82±15.90) showed an upward trend (F=20.94, η²=0.03), and the depressive symptom and NSSI behavior of girls were higher than those of boys (F=19.91, η²=0.02; F=4.57, η²=0.01)(all P < 0.05). The positive predictive relationships between depressive symptom and NSSI behavior among rural left-behind junior high school students [depressive symptom of T1 positively predicted NSSI behavior of T2 and T3 (β=0.10, 0.16); depressive symptom of T2 positively predicted NSSI behavior of T3 (β=0.14), all P < 0.01]. Social support during the T2 period played a partial mediating role between depressive symptom in T1 and NSSI in T3, with a mediating effect of 0.02 (95%CI=0.01-0.17, P < 0.05).

Depressive symptom positively predict the occurrence of NSSI behavior among rural left-behind junior high school students. Social support is an important mediating factor in alleviating the influence of depressive symptoms on the occurrence of NSSI behavior. It should prevent and reduce the occurrence of depression symptoms and NSSI behavior by improving the social support level of rural left behind junior high school students.