Autism Spectrum Disorder (ASD) is a group of serious neurodevelopmental disorders. A significant comorbidity exists between ADHD and ASD: 30%-50% of individuals with ASD exhibit ADHD symptoms, and two-thirds with ADHD show ASD traits. Intestinal microbial disturbance is common in children with ASD. A great deal of evidence shows that intestinal microbes can influence the brain to play its role through gut-brain-microbiota axis. We intend to explore the role of Washed Microbiota Transplantation in improving symptoms of children in ASD with or without ADHD; To study the potential etiological mechanism of WMT for the neurodevelopmental disorders.