Abstract: Objective To analyze the relationship between serum vitamin D, total calcium level and bone mineral density(BMD)among children aged 0-5 years old, and to provide a theoretical reference for the prevention and treatment of rickets.Methods From December 2016 to December 2019, 487 children aged 0-5 years old who were admitted to the Xinhui District Second People's Hospital and the Xinhui District Women's Insurance Hospital Pediatric Outpatient Department for normal physical examination were selected.The Z value and abnormal bone mineral density of children with different sex, age, feeding methods, outdoor activities and vitamin D supplementation were compared, and the abnormal rate of bone mineral density(BMD) and bone mineral density(BMD) were observed under different serum 25(OH) D and serum calcium levels. Pearson analysis was used to explore the relationship between serum 25(OH) D, serum calcium level and BMD.Results Of the 487 children, 108 had abnormal BMD, and the abnormal rate was22.18%. With the increase of children's age, the abnormal rate of BMD increased significantly(P=0.038)and the abnormal rate of BMD decreased significantly with the the increase of outdoor activities time(P<0.001). The serum 25(OH) D content increased,and the abnormal rate of bone density gradually decreased(P<0.001). The abnormal rate of bone mineral density(BMD) in children with serum calcium level ≥2.25 mmol/L is lower than that in children with serum calcium level <2.25 mmol(P<0.001). Pearson correlation analysis showed that when the Z value is-1 to 1, the serum 25(OH) D level(r= 0.736) and total calcium level(r=0.0.617) were positively correlated with the Z value(P<0.001).Conclusion The abnormality of BMD in children aged 0-5 years old is more serious. The Z values are positively correlated with serum 25(OH) D and total blood calcium levels, and outdoor activities are expected to reduce the abnormal rate of BMD in children. Vitamin D and supplemental calcium should be supplemented scientifically and reasonably.