Objective To investigate the oral health status of the first-grade primary school students in Shanghai and analyze its influencing factors. Methods In 2021, Huangpu, Xuhui, Jiading, and Jing’an districts were selected in Shanghai by random sampling method. The first-grade students of 8 primary schools in these 4 districts were enrolled by random cluster sampling. Oral clinical examinations and questionnaires were conducted according to the criteria of the Fourth National Oral Health Epidemiological Survey. EpiData 3.1 software was used to create the database. SPSS 26.0 software was applied for statistical analysis. Chi-square test was used to compare the caries prevalence between groups, and two independent samples non-parametric test was used to compare the decayed, missing and filled teeth (DMFT) between groups. Multifactorial logistic regression model was used to analyzse the influencing factors of caries. Results A total of 824 informed consent forms and questionnaires were collected, of which 764 were completed, with an effective rate of 92.7%. The total caries prevalence of the participating students was 65.6% (501/764), and the mean DMFT was 3.24±3.47. A total of 2 473 carious teeth were found in the participating students, and 671 teeth were filled, with a filling rate of 27.1%. There were 7.91±2.76 permanent teeth erupted per student, and 56.3% (430/764) of the students had all 4 first permanent molars erupted. Multivariate logistic regression showed that eating sweets ＞3 times a day (P＝0.030), eating regularly before bedtime (P＝0.001), and parents’ cognition of kids’ poor oral health status (P＝0.025) were the influencing factors for the detection of caries in children. Conclusion The first-grade primary school students in Shanghai have high prevalence of caries. Eating sweets ＞3 times a day, eating regularly before bedtime, and parents’ cognition of kids’ poor oral health status (P＜0.05) are the influencing factors for the detection of caries in children.