Foot entropion is a relatively common congenital malformation of the fetus, which is often underdiagnosed because it is not well understood in the past. Inversion of the foot is a semi-dislocation of the heel dice joint, which fixes the foot in an inward, rotated inversion position. Under normal circumstances, the ultrasound scan shows that the plantar plane and the tibiofibular long axis plane always remain perpendicular and do not show in the same plane. When the heel dice joint is semi-dislocated so that the foot is inversion deformity, on the sonogram, it shows that the plantar bunion and the tibiofibular long-axis section of the lower leg are in the same plane, and after the foot and leg are moving, the two can still be shown in the same plane after several scans, and there is no support or compression from the placenta and the uterine wall around, i.e. no compression by external factors. The main reasons for misdiagnosis of fetal foot entropion are: 1. Due to the limitation of the uterine wall, normal fetal foot also appears in an abnormal entropion position, and the fetus should be made to move and then continue to scan to determine whether the fetal foot can return to its normal position. 2, the fetal activity in late pregnancy is relatively low, which also easily leads to misdiagnosis. Therefore, the best gestational week to check foot entropion during pregnancy is 18-24 weeks, so the fetal size is moderately developed, the amniotic fluid is sufficient, and the limbs are clearly displayed. The detection rate of this type of fetal anomaly in prenatal screening can only be improved by enhancing the understanding of clubfoot in clinical practice.