Autism Spectrum Disorder (ASD) is a group of serious neurodevelopmental disorders. Intestinal microbial disturbance is common in children with ASD, and about 40% of ASD children suffer from gastrointestinal dysfunction. A great deal of evidence shows that intestinal microbes can influence the brain to play its role through "brain-intestinal-microbiota axis". Fecal microbial biota transplantation (FMT) is the most direct way to change the intestinal flora rapidly. We intend to study the difference of intestinal flora structure and metabolism between ASD children and control children at the level of phylum, genus and species; To explore the role of fecal bacteria transplantation in improving core symptoms and gastrointestinal dysfunction of children in autism spectrum disorder; To study the potential etiological mechanism of autism spectrum disorder.