Objective: To analyze the status of serum 25 hydroxyvitamin D[25 (OH)D] in children aged 0-6 years in Gansu Province, and to analyze the relationships between 25 (OH)D and age, seasonal characteristics and physical development, so as to provide a scientific reference for supplementing vitamin D for children in due time. Methods: Stratified random cluster sampling method was used to select a total of 9 790 children aged 0-6 years from 6 cities and prefectures maternity and child health institutions in Gansu Province for health examination from January 2019 to December 2020. Serum 25 (OH)D concentration from 1 mL peripheral blood was tested by enzyme linked immunoassay. Subjects were classified into overweight and normal figure groups based on weight for height. Results: the serum 25 (OH)D level M(P 25 ,P 75 ) of the children aged 0-6 was 81.31(63.14, 95.86)nmol/L. The detection rate of 25 (OH)D deficiency and insufficiency was 45.11%. The serum 25 (OH)D level of children 4- 6 years old was significantly lower than that of infants <1 year old and children 1-<4 years old, and the detection rate of 25 (OH)D deficiency and insufficiency was highest among 4-6 years old( χ 2=83.67, P <0.05). In winter the proportion of 25 (OH)D insufficiency and deficiency was highest (55.82%) ( χ 2=194.12, P <0.01). For overweight children, the abnormal rate of 25 (OH)D (19.83%) was significantly higher in autumn ( P <0.01). Conclusion Children s vitamin D levels were associated with age, season and physical development. Vitamin D surveillance should be focused on ages less than 1 year old and above 4 years old, winter should be an important season. For overweight children, autumn should be the focus period for vitamin D deficiency prevention.