There are many reasons for the formation of harelip, and it has a certain degree of heredity. Generally speaking, the formation of harelip is basically decided during fetal development and is more related to genetic factors. There is also a relationship with environmental factors, which can cause fetal developmental malformations if the fetus is affected by viral infections or radiation or bad emotions during pregnancy. Therefore, during the important period of 6~8 weeks of pregnancy, we should try to avoid the influence of external environmental factors and do ultrasound examination in time to detect the abnormalities. It is also important to identify whether chromosomal abnormalities are combined.