Abstract: Objective To analyze the Vitamin D levels and analysis of related risk factors in 5 132 children under 6 years old in Weifang area, and to provide reference for prevention and treatment of diseases related to vitamin D deficiency or unsufficient. Methods A total of 5 132 children under 6 years old examined in our hospital from August 2016 to August 2018 were selected as research subject. The serum 25-hydroxyvitamin D[25-(OH)D] levels of children were determined by enzyme-linked immunosorbent assay. The nutritional status of vitamin D in children were analyzed from the aspects of gender, age and season. The possible risk factors were analyzed by single factor and logistic multiple regression analysis. Results The vitamin D deficiency rate was 10.76% in children under 6 years old, and the unsufficient rate was 16.62%. The serum 25-(OH)D levels, vitamin D deficiency rate, and unsufficient rate were not significantly different between boys and girls under 6 years of age(all P>0.05). The vitamin D deficiency rate and unsufficient rate in children aged 3 to 6 years old is higher than 0-1 years old, 1-2 years old, 2-3 years old(all P<0.05), and the serum 25-(OH)D levels of 3-6 years old is was lower than 0-1 years old, 1-2 years old, and 2-3 years old(all P<0.05). The vitamin D deficiency rate and unsufficient rate in summer and autumn were significantly lower than those in spring and winter(P<0.05). The risk factors affecting vitamin D deficiency or unsufficient in children under 6 years old were chaotic or not taking vitamin D preparation, breastfeeding alone, outdoor exercise<2 hours/day, low maternal education, repeated upper respiratory tract infection, Repeated diarrhea, picky or anorexia and repeated bronchial asthma. Conclusion The deficiency or unsufficient rate of vitamin D is 27.38%, which is related to age and season. The deficiency or unsufficient of vitamin D is mainly concentrated in the age of 3-6 years and spring and winter. The main influencing factors are feeding mode, outdoor sports, picky or anorexia, vitamin D preparation, mother culture, repeated upper respiratory tract infection, repeated diarrhea and repeated bronchial asthma.