Objective: To investigate the prevalence of flat feet and associated factors in school aged children in Kunming City, to provide evidence supporting the prevention of flat feet. Methods: From December 2021 to February 2022, 4 444 children aged 7-13 in five primary schools in Kunming were screened for flat feet with the optical foot assessment and recording device. The incidence of flatfoot was counted, and Logistic regression was used to analyze the influencing factors of flatoccurrence. Results: The overall prevalence rate was 29.10%, of which 21.79% were mild, 52.43% were moderate, 25.78% were severe, 89.10 % were bipedal, and 10.90% were monopedal. The prevalence rates in the 7-year old and 13-year old groups were 36.91% and 10.43%, respectively, and the risk in the former was 5.00 times that in the latter( OR=5.00, 95%CI =3.22-7.52). The prevalence rates in rural and urban students were 38.53%, 22.46%, respectively, and the risk in the former was 2.17 times that in the latter( OR=2.17, 95%CI =1.90-2.47). The prevalence of flat feet in male and female students were 34.21%, 23.29%, respectively, and the risk in male students was 1.71 times higher than that in female students( OR=1.71, 95%CI =1.50-1.95). The incidence of flat feet correlated with BMI, and the risk of flat feet was higher in the group with overweight and obese groups than normal( OR=1.31, 1.10, P < 0.01). Conclusion The prevalence of flat feet in school age children aged 7-13 years decreased with age. The prevalence and risk of flat feet is lower in girls than boys, and the incidence and risk of flat feet are lower in urban than rural children. The incidence of flat feet in most children is moderate, and the risk increased with increasing BMI. For school aged children with flat feet, early prevention, detection and treatment are needed.