Objective To examine the effects of sleep quality and psychological resilience on the relationship between peer relationship and loneliness in adolescents with mixed anxiety and depressive disorder （MADD）. Methods A total of 265 adolescents diagnosed with MADD， who visited or were hospitalized in the Unit of Child and Adolescent Psychology of Daqing Third Hospital from September 2020 to June 2021， were selected as the research subjects by convenience sampling method. Adolescent Peer Relationship Scale， University of California， Los Angeles （UCLA） Loneliness Scale， Resilience Scale for Children and Adolescent （RSCA）， Pittsburgh Sleep Quality Index （PSQI） were used to investigate. Pearson correlation was used to analyze the correlation among peer relationship， loneliness， sleep quality and psychological resilience of MADD adolescents. The model 6 in SPSS PROCESS macro program was a used to test the mediating effect. A total of 280 questionnaires were distributed in this study， and 265 valid questionnaires were collected， with an effective response rate of 93.00%. Results The score of the Adolescent Peer Relationship Scale in MADD adolescents was （59.69±12.93）， the score of the UCLA Loneliness Scale was （56.49±10.83）， the RSCA score was （67.68±15.72）， and the PSQI score was （10.31±3.92）. In MADD adolescents， sleep quality was positively correlated with peer relationship， sleep quality with loneliness， and peer relationship with loneliness （r=0.49， 0.50， 0.76； P＜0.01）， while psychological resilience was negatively correlated with peer relationship， loneliness， and sleep quality （r=-0.65， -0.69， -0.47； P ＜ 0.01）. Psychological resilience played a partial mediating role in the relationship between peer relationship and loneliness in adolescents with MADD. The mediating effect consisted of three pathways： peer relationship-sleep quality-loneliness； peer relationshipresilience-loneliness； peer relationship-sleep quality-resilience-loneliness. The effect value of these three pathways accounted for 6.94%， 21.73% and 3.93% of the total effect， respectively. The total indirect effect accounted for 32.59% of the total effect. Conclusions In addition to directly influencing the sense of loneliness of adolescents with mixed anxiety and depression disorder， peer relations also indirectly affect the sense of loneliness through the mediation of sleep quality and psychological resilience， and the chain mediation of sleep quality and psychological resilience.