The social responsibility of college students in the later stages of adolescence for sustainable development is emphasized, and the role of universities has become a crucial task. This study aimed to explore the level of college students' cognition, attitude, and behavior towards sustainable development and the association among them through the moderation effect of informal online learning. The difference verification and structural equation modeling were applied to 559 students who majored in science, and statistical validity was confirmed. Regarding the sustainable development level of college students, there was a significant difference in cognition, attitude, and behavior towards sustainable development between males and females, formal education, and informal online learning. Further, college students' attitudes towards sustainable development played a significant mediating role between cognition and behavior. The study also found a significant moderation effect of informal online learning on students' cognition and attitude toward sustainable development behavior. Accordingly, this study suggests that universities should systematically design educational programs to promote college students' behavioral change toward sustainable development through personal life-oriented learning courses.