This cross-sectional study examined the relationship between sleep quality, sleep duration, and dietary disorder severity among 982 adolescents in Xiamen, China. Using validated questionnaires and multivariate statistical analyses, the study found that poorer subjective sleep quality and shorter sleep duration were significantly associated with higher levels of dietary disorder. Adolescents with excellent sleep quality were 58% less likely to experience dietary disorder, while those with sleep curtailment (<8 hours per night) were 82% more likely to exhibit disordered eating behaviors. Nonlinear analyses revealed threshold effects, showing that dietary disorder risk increased as sleep quality declined and sleep duration shortened, particularly within the 6–9 hour sleep range. Additional risk factors included older age, urban residence, higher BMI, and lower maternal education level. The findings highlight sleep health as a critical and modifiable factor influencing adolescent dietary behaviors and support the integration of sleep hygiene interventions into nutrition and public health strategies targeting youth.