ObjectiveTo explore the mental health status and its influencing factors among middle school students in Xide County， Liangshan Yi Autonomous Prefecture， and to provide references for mental health interventions for local middle school students. MethodsUsing a cross-sectional study design， one junior middle school and one senior middle school in Xide County， Liangshan Prefecture， Sichuan Province， were randomly selected on September 16， 2021， and two classes per grade in each school involving 288 students were recruited. Subjects were assessed using Patients' Health Questionnaire Depression Scale-9 item （PHQ-9）， Generalized Anxiety Disorder Scale-7 item （GAD-7）， PTSD Checklist for DSM-5 （PCL-5）， Multidimensional Scale of Perceived Social Support （MSPSS） and UCLA Loneliness Scale （ULS-3）. Then the scores of above scales were compared among middle school students with different demographic characteristics， and binary Logistic regression analysis was conducted to screen the influencing factors of post-traumatic stress disorder (PTSD） symptoms. ResultsAmong the respondents， 17.71% （95% CI： 0.133~0.221）， 8.68% （95% CI： 0.054~0.120）， 2.78% （95% CI： 0.009~0.047） and 45.83% （95% CI： 0.400~0.516） were reported to have symptoms of depression， anxiety， PTSD and loneliness， respectively. Students in senior middle school scored lower on PCL-5 and ULS-3 than those in junior middle school ［（6.46±8.91） vs. （8.87±9.42）， t=2.202， P<0.05； （4.67±1.65） vs. （5.60±1.88）， t=4.431， P<0.01］. Regression analysis denoted that depressive symptoms （OR=7.630， P<0.05） and anxiety symptoms （OR=3.789， P<0.01） were risk factors for PTSD symptoms among middle school students. ConclusionThe middle school students in Xide County， Liangshan Yi Autonomous Prefecture suffer a high prevalence rate of depressive symptoms and loneliness， and those in junior middle school are more likely to feel a sense of strong loneliness， furthermore， depressive symptoms and anxiety symptoms are risk factors for PTSD symptoms.