Objective: To analyze the epidemiological characteristics and influencing factors of flatfoot among primary and middle school students in Inner Mongolia. Methods: A survey was conducted among 2,800 primary and middle school students in Inner Mongolia. The foot arch and plantar pressure of the subjects were measured using the footprint method and the FootcanUSB plantar pressure testing system, respectively. The incidence of flatfoot among primary and middle school students was statistically analyzed, and regression analysis was used to analyze the influencing factors of flatfoot occurrence. Results: Among the 2,800 students, 867 cases of flatfoot were detected, with a detection rate of 30.95%. The proportions of mild, moderate, and severe flatfoot were 21.12%, 46.23%, and 31.62%, respectively. The detection rates of flatfoot among males and females were 20.04% and 10.93%, respectively, with the male detection rate significantly higher than that of females (P < 0.05). The detection rates of flatfoot among students aged 7 to 14 years old were 49.42%, 42.18%, 40.34%, 35.78%, 28.49%, 23.33%, 15.79%, and 11.95%, respectively. The detection rates of flatfoot varied among students of different ages, and the detection rate gradually decreased with increasing age. Weight, household registration, extracurricular activities, and shoe type were all influencing factors of flatfoot occurrence among primary and middle school students, in addition to BMI and physical exercise (P < 0.05). The risk and protective factors for flatfoot occurrence among primary and middle school students were BMI and physical exercise, respectively (P < 0.05). Conclusion: The incidence of flatfoot is relatively high among primary and middle school students in Inner Mongolia. Relevant factors for the occurrence of flatfoot include weight, household registration, and physical exercise. To reduce the occurrence of flatfoot, it is recommended to control weight and engage in regular physical exercise.