Objective To study the diagnostic value of the lower limb line in evaluating the development of infants in hip sonograms, and to provide reference for clinicians to determine the development of infant hip. Methods The Graf method was used to examine 863 infants, and observe the relationship between the lower limb line and the femoral head in different types of infant’s hip sonograms. and the sensitivity, specificity, positive predictive value and negative predictive value of the lower limb line were calculated respectively. Results In 1726 infants hip sonograms, the sensitivity of the lower limb line in diagnosing infant’s hip dislocation was 78.7%, specificity 89.3%, positive predictive value 21.2%, negative predictive value 99.1%. The sensitivity of the lower limb line in diagnosing infant’s hip immature was 25.4%, specificity 97.3%, positive predictive value 88.9%, negative predictive value 60.7%. For one baby, whose hip is negative of the lower limb line developed better than another hip which is positive of the lower limb line. Conclusions Detecting an infant’s hip with the Graf method, the lower limb line is added to judge whether the femoral head is shifting in the acetabulum, which is helpful for clinicians to judge the development of the infant’s hip more comprehensively.