Fragile X syndrome is an X-linked dominant disorder, a pre-gene mutation, and one of the chromosomal genetic disorders. Clinical manifestations of intellectual disability, intelligence significantly behind their peers, large testicles, congenital deafness, poorly expressed speech, mental retardation, and difficulty in self-care. If phenotypically normal male pre-mutation wide gene transmission of the next generation at least 50%, no clinical symptoms of the pre-mutation of the female carriers in the transmission of the next generation as much as 80%. Therefore, in order to avoid the occurrence of this disease, it is important to focus on prenatal screening and diagnosis is very important, prenatal diagnosis and selective abortion is the main means of prevention of this disease.