To improve eugenics to determine the condition of the fetus in utero is called prenatal screening or prenatal diagnosis, which includes a variety of methods, and ultrasound plays an irreplaceable role in prenatal diagnosis. Early and mid-trimester serological tests are mainly limited to screening for chromosomal abnormalities, and genetic diagnostic methods such as amniotic fluid and umbilical cord blood sampling have a small scope of application and are only applicable to cases where chromosomal abnormalities are suspected. Down’s syndrome screening can be done for everyone and is non-invasive, but amniotic fluid extraction for people at high risk for the test is somewhat damaging. Magnetic resonance images are much clearer than ultrasound, but cannot be used for screening, only for fetuses suspected of having problems. Ultrasound is indicated for all populations and is screening for some abnormalities and diagnostic for others, ranging from the central nervous system, digestive tract, urinary tract, skeletal and many other systems. Although ultrasound cannot diagnose chromosomal abnormalities, it can detect most chromosomal abnormalities combined with structural malformations. For morphologic structural alterations as well as certain functional alterations, ultrasound can be observed. There are also some structural abnormalities fetus chromosomes are normal and cannot be screened by Down’s screening, but can be diagnosed by ultrasound, even can be serious abnormalities, for example: congenital heart disease, some of them are chromosomal abnormalities, but most of them are normal chromosomes, then only ultrasound can screen out congenital heart disease in this case. So ultrasound still plays a big role in prenatal diagnosis, especially for screening of all people, convenient, non-invasive, highly acceptable to patients, inexpensive, and more intuitive to observe changes in fetal morphological structure and functional structure. The role of prenatal diagnosis in reducing birth defects is related to the quality of the national population at birth.