To determine the normal range of the inner diameters of the anatomical structures in the fetal cardiovascular system during the second trimester in Ningxia and to investigate their variation with gestational age. Routine echocardiography was performed for 1 247 normal fetuses during the second trimester (22~28 weeks) to determine the inner diameters of the atrium, ventricle, foramen ovale, aorta, pulmonary artery, left/right pulmonary artery, aortic isthmus, descending aorta, and ductus arteriosus. Measurement data were grouped by gestational age, and the correlation between the measurement data and gestational age was investigated. The inner diameters of the fetal atria, ventricles, and great vessels increased with gestational age and were significantly associated with gestational age (P < 0.05). In Ningxia, determining the normal range of fetal cardiovascular diameters during the second trimester allows the evaluation of fetal cardiovascular system development and provides an important basis for the accurate identification of fetal congenital heart disease.