Objective To explore the relationship between the symptom severity of attention deficit hyperactivity disorder （ADHD） and obesity in school-age children. Methods A total of 60 school-age children with ADHD who were admitted to Qingdao Mental Health Center and met DSM-5 diagnostic criteria were selected as subjects. The self-made basic demographic characteristics questionnaire and Conners Parental Symptom Questionnaire were used to evaluate and calculate the body mass index （BMI）. According to the BMI， the children were divided into obese group and non-obese group. The scale scores and obesity degree of the two groups were compared， and the relationship between the severity of ADHD symptoms and obesity degree was analyzed. Results The total score of Conners Parental Symptom Questionnaire in obese group was significantly higher than that in non-obese group ［（73.46±6.75） vs （58.02±5.70）， t=9.317， P ＜ 0.05］， among which the score of conduct problem ［（15.00±0.98） vs （13.03±1.78）， t=4.943， P ＜ 0.05］， impulse-hyperactivity ［（10.25±1.51） vs （9.25±1.42）， t=2.996， P＜ 0.05］， and hyperactivity index ［（23.17±2.50）］ vs （20.30±2.80）， t=4.947， P＜ 0.05］ were significantly higher than those of the non-obese group. The correlation test was made between the Percentile of BMI and each factor score of Conners Parental Symptom Questionnaire and the results showed a positive correlation （r=0.559， 0.404， all P＜ 0.05）. Binary Logistic regression analysis showed that conduct disorder （OR=3.371， 95%CI： 1.389-8.181） and anxiety （OR=1.325， 95%CI： 0.947- 1.853） were independent risk factors for obesity （all P＜ 0.05）. Conclusions The severity of ADHD symptoms is correlated with obesity in school-age children， and the severity of ADHD symptoms may affect the weight of children.