Cooperation skills are fundamental for student development. To enhance these skills effectively, understanding their influencing factors is essential. Drawing on data from the Survey on Social and Emotional Skills (SSES) 2019 China Suzhou Survey, this study examines how interpersonal relationships influence adolescent students' cooperation skills. It was found that the father-child relationship, mother-child relationship, classmate relationship, teacher-student relationship, and neighborhood relationship all positively affected adolescent students' cooperation skills, after controlling students' gender and family's socio-economic status. Notably, relationships with classmates emerge as the most significant contributors to students' cooperation skills, demonstrating significant interaction effects with mother-child relationship, father-child relationship, teacher-student relationship, and neighbourhood relationship. The discussion and application of the findings enhance the cultivation of students' cooperation skills effectively, thereby equipping students with essential capabilities for success in the 21st century.