Objective: Analysis of the difference between fetal malformations and the age of pregnant women by the prenatal ultrasonography. Methods: 6119 cases of pregnant women were accepted prenatal ultrasonography, according to age into ≤19 years, 20 to 24 years, 25 to 29 years, 30 to 34 years, 35 to 39 years and ≥ 40 years six groups. The cases of fetal malformations which were compared with the results of prenatal diagnosis center’s examination, the postnatal newborn examination or necropsy specimens after termination of pregnancy were correct by the prenatal ultrasonography. They were analysed the six kinds of serious malformations, the number and types of fetal malformations according to various groups. Results: There were 205 cases fetal malformations in 6119 pregnant women, 186 cases were diagnosed correctly by Ultrasonography. The detection rate of six serious malformations of ≤ 19 years group was the highest. The difference was statistically significant (P< 0.05).The detection rate of Multiple malformations of ≥ 40 years was the highest. The congenital cardiac malformations was highest in the types of fetal malformations, followed by nervous system malformations, facial malformations. Conclusion: Women who are too small to be prone to be detected serious fetal malformations, women who are too old to be prone to be detected multiple malformations, and the probability of nervous system malformations and congenital cardiac malformations is higher than other pregnant women. Therefore the ultrasonic examiner should strengthen on this kind of pregnant women’s prenatal ultrasonography to avoid misdiagnosis and missed diagnosis of fetal malformations.