["Child &Family Social Work, EarlyView. ", "\nABSTRACT\nRural Chinese adolescents face significant mental health challenges shaped by cumulative risks across ecological systems, particularly individual, family and peer domains. However, the underlying mechanism linking cumulative risk to mental health problems remains insufficiently explored. A total of 1390 junior high school students (49.4% female; M age = 13.40 ± 1.10 years) from a rural area in Sichuan Province, China, participated in two survey waves. A cumulative risk index (CRI; range 0–10) was created by summing 10 binary risk factors across individual, family and peer domains. This study examined loneliness as a mediator and investigated moderated mediation by family functioning. Results indicated that higher cumulative risk exposure was significantly associated with increased mental health problems among rural adolescents. Loneliness emerged as a key mediator in the relationship between cumulative risk and mental health problems. Family functioning served as a protective factor, attenuating both the direct and indirect effects of cumulative risk on mental health problems. This study highlighted the pressing need to address cumulative risk among rural adolescents while leveraging family functioning as a buffering factor. Interventions that strengthen family dynamics and reduce loneliness may offer practical strategies for mitigating mental health problems in this vulnerable population.\n"]