Objective: To investigate the moderating effect of health literacy on the association between insomnia and non suicidal self injury (NSSI) behaviors among college freshmen, so as to provide evidence for improving interventions targeting NSSI behaviors. Methods: A longitudinal survey was conducted among 5 615 college freshmen selected from three colleges in Hefei, Huainan and Anqing cities of Anhui Province by cluster sampling (T0:May-June 2024; T1:October-December 2024). The Chinese version of the Insomnia Severity Index, Chinese Adolescent Interactive Health Literacy Questionnaire, and Adolescent Non suicidal Self injury Assessment Questionnaire were used to assess students insomnia, health literacy, and NSSI behaviors, respectively. Between group comparison was performed with the Chi square test, and the PROCESS macro (Model 1) was used to analyze the moderating role of health literacy in the association between insomnia and NSSI, and simple slope analysis was employed to further elucidate the pattern of the moderating effect. Results: The report rate of NSSI behaviors among college freshmen was 2.96 % at T1. The detection rate was significantly higher among boys, students with poorer family economic status, those with fewer close friends and those who were only children than in the corresponding comparison groups, with all differences statistically significant ( χ 2=5.13-39.56, all P <0.05). The results of the moderation analysis indicated that insomnia at T0 positively predicted NSSI behaviors at T1 among college freshmen ( OR=1.44, 95%CI =1.22-1.69), whereas health literacy at T0 negatively predicted NSSI behaviors at T1 ( OR=0.73, 95%CI =0.62-0.86); the interaction term of the two also significantly predicted NSSI behaviors ( OR=1.16, 95%CI =1.03-1.30) (all P <0.05). At low levels of health literacy, insomnia at T0 showed a positive predictive effect on NSSI behaviors at T1 ( B=0.22, 95%CI =0.06-0.38); at high levels of health literacy, the positive predictive effect of insomnia at T0 on NSSI behaviors at T1 remained statistically significant ( B=0.51, 95%CI =0.28-0.74) (both P <0.05). Conclusions Health literacy plays a significant positive moderating role in the association between insomnia and NSSI behaviors among college freshmen. NSSI behaviors interventions should address health cognition problems while enhancing individuals health literacy.