Bipolar disorder（ BD） is a common affective disorder in children and adolescents and is frequently co-morbid with other mental disorders. Comorbidity often poses significant challenges to the diagnosis， treatment， and prognosis of diseases. This paper reviews the epidemiology， clinical characteristics， and treatment of comorbidities of mental disorders in children and adolescents， including BD， attention deficit/ hyperactivity disorder， autism spectrum disorder， obsessive compulsive disorder， and substance use disorder， aiming to provide reference for clinical diagnosis and treatment.