Objective:To analyse the characteristics and clinical application of routine electroencephalogram combined with e-vent-related potential P300 in patients with attention deficit and hyperactivity disorder.Methods:Selected 50 patients with attention def-icit as the attention deficit group,50 patients with hyperactivity disorder as the hyperactivity disorder group,and another 50 healthy indi-viduals for physical examination as the control group.All patients in each group underwent general data statistics and routine EEG and event-related potential P300 examinations to obtain the latency,amplitude,8 wave,θ wave,α wave amplitude and frequency of Pz,Cz,and Fz,as well as abnormal EEG conditions.Results:There were no significant differences in gender,age,body mass index,educational level,and malnutrition among the three groups(P＞0.05).Compared with the control group,the attention deficit group and hyperactivi-ty disorder group had a higher proportion of patients with a history of traumatic brain injury and lower MoCA scores(P＜0.05).There was no significant difference in the history of traumatic brain injury and MoCA score between the attention deficit group and the hyper-activity disorder group(P＞0.05).Compared with the control group,patients with attention deficit and hyperactivity disorder had high-er levels of latent periods of Pz,Cz,and Fz,lower levels of wave amplitudes,higher rates of EEG abnormalities,and higher levels of am-plitude of δ,θ,and α waves(P＜0.05).There was no significant difference in the latency and amplitude of Pz,Cz,and Fz,as well as the amplitude levels of δ,θ,and α waves,and the proportion of abnormal EEG between the attention deficit group and the hyperactivity disorder group(P＞0.05).There was no significant difference in the frequency levels of the three groups of δ wave,θ wave,and αwave(P＞0.05).The ROC curve showed that compared with the single diagnosis of event-related potential P300 and conventional e-lectroencephalogram,the combined detection had higher sensitivity and accuracy in diagnosing attention deficit and hyperactivity disor-der(P＜0.001).Conclusion:Patients with attention deficit and hyperactivity disorder have higher latent periods of Pz,Cz,and Fz,ab-normal rates of EEG,and higher levels of amplitude of δ,θ,and α waves,while lower levels of amplitude of Pz,Cz,and Fz waves.The diagnostic value of routine EEG combined with event-related potential P300 for attention deficit and hyperactivity disorder is relatively high.