This article examines the clinical application of the ICD-11 Clinical Descriptions and Diagnostic Requirements (CDDR) for Mental, Behavioural and Neurodevelopmental Disorders in the diagnosis and assessment of mood disorders in children and adolescents. It systematically reviews key updates in the ICD-11 CDDR, including shifts in classification from a categorical to a spectrum-based approach, refined diagnostic criteria for depressive and bipolar disorders, and the introduction of Disruptive Mood Dysregulation Disorder (DMDD). Emphasis is placed on the importance of adopting a developmental perspectives, clarifying symptom definitions, and differentiating between chronic irritability and episodic mood episodes. A structured clinical assessment and diagnostic workflow is proposed to enhance diagnostic accuracy and support targeted interventions. The article concludes with recommendations for training, localized research, and clinical integration to facilitate the effective implementation of ICD-11 CDDR in China.