Objective: To explore the relationship between sleep quality and mental health among middle school students, so as to provide scientific basis for improving mental health among adolescents. Methods: From September to December 2023, a stratified cluster random sampling method was employed to select 5 713 middle school students aged 13-18 from Shanghai, Suzhou, Taiyuan, Wuyuan, Xingyi, and Urumqi. Sleep quality and mental health were assessed using the Pittsburgh Sleep Quality Index (PSQI) and the Brief Adolescent Mental Health Assessment Questionnaire. Spearman correlation analysis and linear regression analysis were used to explore the relationship between sleep quality and various dimensions of mental health among middle school students. Results: There was a statistically significant difference in the total PSQI score among middle school students of different age groups ( H=226.49, P <0.01), and there was no statistically significant difference in the psychological health scores of middle school students in different age groups ( H=5.37, P >0.05). In terms of gender, the total PSQI score for girls [5.00 (3.00, 6.00)] was higher than that for boys [4.00 (2.00, 6.00)]; additionally, boys had higher mental health scores [85.00 (75.00, 90.00)] than females [83.00 (70.00, 89.00)], with statistically significant differences ( Z=-10.90, -8.16, P <0.01). Spearman correlation analysis revealed a negative correlation between total PSQI scores and mental health scores ( r=-0.51, P <0.05) among middle school students. After controlling for variables such as maximum oxygen uptake, physical activity and nutritional status, linear regression analysis further confirmed that higher PSQI scores were associated with lower mental health scores ( B=-3.76, 95%CI = -4.15 to -3.38, P <0.01). Conclusion There is a negative correlation between PSQI scores and mental health scores among middle school students, indicating that improving sleep quality may contribute to better mental health among middle school students.