It is a chromosomal disorder, also known as Down syndrome or trisomy 21. It is caused by a problem in the process of germ cell division during embryonic life resulting in the non-separation of chromosome 21. It is associated with the mother’s gestational age, exposure to harmful substances during pregnancy, genetic and viral infections, etc. Clinically, the incidence of trisomy 21 is found to increase with the mother’s gestational age. The child has a special face: wide eye spacing, double external eye corners hanging up, small mouth, half-open mouth, thick tongue often sticking out of the mouth; also accompanied by mental retardation, growth disorders, congenital heart disease, etc. The prevalence of leukemia is about 20 times higher than that of normal children. The diagnosis can be confirmed by chromosome examination. Since there is no specific medical treatment, the main thing is targeted prevention. Women of any age of childbearing should have regular prenatal checkups after pregnancy. Women who are ready to become mothers should avoid giving birth after the age of 40; mothers under the age of 25-30 who have a sick child with trisomy 21 should have their mother’s chromosomes checked, and if they are already pregnant with a second child, cytological examination by amniocentesis can be done to terminate the pregnancy in time for fetuses with chromosomal abnormalities. To avoid the occurrence of this disease.