Objective To ascertain the value of the cardiac axis for the prenatal detection of congenital heart defects. Methods The subjects were clinics and hospitalized pregnant women from 2013 to 2015, gestational age was at 18～40 weeks. Simply randomly selected normal of the fetal heart (group A) and fetal cardiac structural abnormalities (group B) as a control, with 231 cases in group A, group B 36 cases. Fetal cardiac axis was measured on the four-chamber view of the heart. Results Group A had a mean cardiac axis of(37.9±7.6)°, compared with in Group B(52.6±19.8)°(P<0.01).Using above or below the 99％normal range(20.3°～61.9°)of normal group as the abnormal axis,<20.0°was regarded as small of cardiac axis and >62.0°was large. There was no small or large of cardiac axis in group A, and 15 cases of large cardiac axis and 2 cases of small in group B. The difference in two groups of patients with abnormal cardiac axis was statistically significant (P<0.01). The incidence of abnormal cardiac axis of group A was less than group B. Conclusion The measurement of fetal cardiac axis is simple and effect. The presence of a abnormal cardiac axis (<20.0°or >62.0°) in the fetuses is associated with a substantial risk of congenital heart disease. The finding of an abnormal axis should prompt further evaluation of the fetal heart and a detailed anatomical examination.