Objective To study the characteristics of event related potential （ERP） in children with attention deficit hyperactivity disorder （ADHD） and the correlation between ERP and hyperactivity index and intelligence， and to explore the cognitive function of children with ADHD. Methods From June 2019 to December 2020， 61 children with ADHD treated in the outpatient department of Xiamen Xian Yue Hospital were selected as the study group， and 61 healthy children who met the inclusion and exclusion criteria were selected as the control group. ERP and Wechsler intelligence test were performed on children， and Conners Parent Symptom Qeustionnaire （PSQ） was performed on two groups of child caregivers. Results Under target stimulation， the P3 latency of prefrontal region， central region and parietal lobe in the study group was significantly longer than that in the control group， and the difference was statistically significant ［（388.41±47.24） ms vs （372.89±34.75） ms， （395.31±55.18） ms vs （371.33±38.80） ms， （404.23±55.21） ms vs （381.54±38.93） ms； t=2.07， 2.78， 2.62； P ＜ 0.05］. Under target stimulation， there were significant differences in P3 amplitude in prefrontal region， central region and parietal lobe between the two groups ［9.61 （7.60， 15.63）μV vs 13.52 （10.04， 16.90）μV， 11.20 （5.81， 17.43）μV vs 13.49 （9.22， 16.54）μV， 12.33 （7.05， 18.85）μV vs 14.74 （9.31， 20.09）μV； Z=-2.77， -2.10， -2.06； P ＜ 0.05］. There were significant differences in speech comprehension index， perceptual reasoning index， working memory index， processing speed index and total IQ scores between the two groups ［98.0 （89.0， 103.5） vs 99.0 （95.5， 107.0）， 94.0 （86.0， 103.0） vs 100.0 （89.0， 109.0）， 85.0 （75.0， 97.0） vs 91.0 （87.0， 97.0）， 83.0 （77.0， 95.0） vs 92.0 （80.5， 99.0）， 83.0 （77.0， 95.0） vs 92.0 （80.5， 99.0）； Z=-2.10， -2.54， -3.70， -3.33， -2.86； P＜ 0.05］. The hyperactivity index score of the study group was higher than that of the control group ［1.80 （1.60， 2.10） vs 0.80 （0.65， 1.15）； Z=9.54； P＜ 0.05］. Correlation analysis results showed that the latency of P3 was negatively correlated with working memory index （WMI） and processing speed index （PSI） （r=-0.29， -0.26， P ＜ 0.05）. The peak-to-peak value of N2P3 was positively correlated with PSI （r=0.30， P ＜ 0.05）. Conclusions ADHD children have a certain degree of cognitive dysfunction， ERP can measure the cognitive function of ADHD children， and the combined use of ERP and Wechsler intelligence is conducive to an objective and comprehensive evaluation of ADHD.