(1) Genetic factors. Many studies have shown that ADHD is a familial disease with complex genetic characteristics, with an average heritability of 0.76, suggesting that the genetic factor is ADHD. Etiology plays a major role. \x0d\ (2) Organic factors. Slight brain injury caused by various reasons during pregnancy, perinatal period and after birth may be the cause of this disorder in some children, but not all children with this disorder have brain injury, and not all children with this injury suffer from this disease. Many children have no evidence of brain injury. \x0d\ (3) Neuroanatomical factors. Magnetic resonance research reported that the corpus callosum and caudate nucleus decreased in children with this disorder, and functional magnetic resonance research also reported that the metabolism of caudate nucleus, frontal lobe and anterior cingulate gyrus decreased. \x0d\ (4) Neurophysiological factors. The abnormal rate of EEG in children with this disease is high, mainly due to the increase of slow wave activity. Analysis of EEG power spectrum shows that slow wave power increases, α wave power decreases and average frequency decreases. It is suggested that the children with this disease have delayed development of central nervous system or insufficient awakening of cerebral cortex. \x0d\ (5) Neurobiochemical factors. Studies have shown that this disorder may be related to the metabolic disorder and dysfunction of central neurotransmitters, including: the renewal rate of dopamine and adrenaline decreased, and the function of dopamine and norepinephrine decreased. \x0d\ (6) Psychosocial factors. Excessive development of early intelligence, heavy learning burden, bad social environment and family environment, such as poor economy, broken parents' feelings, improper education methods, etc., will increase the risk of children suffering from ADHD. \x0d\ (7) Other factors. This disorder may be related to zinc and iron deficiency and elevated blood lead. Food additives may increase the risk of ADHD in children.