Objective To explore The early natural history of hip joint in premature infants.Methods A prospective study was conducted to collect 393 premature infants and 3709 full-term infants born in Yangzhou maternal and child care service centre from January 2019 to June 2021. Graf’s hip ultrasonography was performed on 1, 7, 42 and 90 days after birth to observe the early development and prognosis of hip joint. Results The weight of preterm infants was lower than that of full-term infants（P<0.05）, the rest risk factors of DDH were not statistically significant（P>0.05）. The proportion of type I hip joint in preterm infants was higher than that in full-term infants at 1 and 7 days after birth（P﹤0.05）, but there was no significant difference between the two groups at 42 days（P>0.05）. The proportion of type I hip joint in late preterm group was lower than that in very preterm and moderate preterm group at 1 and 7 days after birth（P﹤0.05）, but there was no significant difference among the three groups at 42 days（P﹥0.05）. In the preterm group, 74 cases of type Ⅱa hip joints were all converted to typeⅠ at 90 days. In the full-term infant group, 1128 cases of type Ⅱa hip joints were transformed into typeⅠ, and the rest 20 cases were transformed into type Ⅱb, but the difference was not statistically significant at 90 days (P > 0.05). The α-angle in premature group was higher than that of full-term group, and increased with growth（P﹤0.05）. The β-angle in premature group was lower than that of full-term group, and decreased with growth（P﹤0.05）.Conclusion The proportion of type I hip joints in preterm infants is higher than that in term infants at birth, and the proportion of type I hip joints in late preterm infants is lower than that in very preterm and moderate preterm infants. Most of type Ⅱa hip joints in preterm infants can be converted to type I hip joints with growth. It is reasonable that the first screening time for preterm infants can be choosed at 42 days after birth.