Down syndrome, also known as trisomy 21 or Down syndrome, is a chromosomal abnormality that causes abortions in 60% of children in early fetal life. 60% of survivors have significant mental retardation, peculiar facial features, growth retardation, and multiple malformations. The severity of the disease is related to the percentage of heterosexual karyotype. 1, special face: at birth, there can be a more obvious special face, dull expression, small eye fissure, wide eye spacing, both eyes canthus upward, there may be inner canthus, low nasal bridge, small external ear, narrow hard jaw, often open mouth and tongue, salivation, small and round head, large fontanelle and delayed closure, short and wide neck, often drowsy and feeding difficulties. 2, intelligent backwardness: this is the most prominent and serious clinical manifestation of the disease, the vast majority of children have different degrees of intelligent development disorders, children with low intelligence performance with age and gradually obvious, IQ 25 to 50. chimeric children whose behavior and action tend to stereotyped, abstract thinking ability is the most impaired. 3. Growth retardation: The growth and weight of the child at birth are lower than normal, postnatal physical development and movement development are delayed, short stature, bone age lags behind the actual age, late teething and abnormal sequence. Short limbs, underground muscle tone. 4. Late sexual maturity: male patients are infertile for life, female patients will have menstruation at puberty and may have the possibility of having offspring. 5, skin literary features: through the hand, hand palm lines atd angle enlargement, etc. 6, with other deformities: 30% of children with congenital heart disease, digestive tract deformities, etc. 7, the immune system is under, prone to various infections: the chance of developing leukemia tens of times than normal people. Patients who survive to the age of 30 often develop symptoms of Alzheimer’s disease.